Wide-angle glasses-free 3-D image display system without ghosting providing real depth and agreement between accommodation and convergence

ABSTRACT

An image display system provides a viewer with an experience of three-dimensional imagery by presenting a composite image made up of at least two separate images. The system includes at least first and second image sources, a beam combiner, and a “background-image-occluding element” which prevents background imagery from being seen through foreground image elements. The system presents the image from one of the image sources, containing background image information, at a distance from the viewer which is greater than the distance from the viewer to the other image presented from the other image source, which contains foreground image elements. The “background-image-occluding element” is positioned at the same optical distance from the viewer as the image containing foreground image elements, eliminating any parallax error between them, enabling the foreground image elements to always occlude appropriate areas of the background image, regardless of the viewer&#39;s position or the background image brightness relative to the brightness of foreground image elements.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/384,215, issuing as U.S. Pat. No. 7,492,523, which is a divisional ofU.S. patent application Ser. No. 10/045,830, filed Oct. 20, 2001, issuedas U.S. Pat. No. 7,016,116, which is a continuation of U.S. patentapplication Ser. No. 08/774,569, filed Dec. 31, 1996, issued as U.S.Pat. No. 6,310,733; the aforementioned application claiming prioritybenefit under 35 U.S.C. § 119(e) from U.S. Provisional PatentApplication 60/023,677, filed Aug. 16, 1996, the entire disclosures ofeach of the aforementioned documents being herein incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to image display systems, includingtechnology for the creation of aerial real images and otherthree-dimensional (3-D) effects. More particularly, the presentinvention involves improved imaging systems, especially useful forcomputer displays and videoconferencing. More particularly, the presentinvention involves improved imaging systems, capable of providingmultiplane images from video or other sources that simulate theperception of 3-D real depth. The present invention also has thecapacity to provide, simultaneously or alternately, multiple images suchas for multiple players of a video game.

Numerous attempts have been made over several decades to devise apractical system for 3-D video, as well as 3-D photography in general.The prior art discloses no satisfactory methodology that producesaffordable 3-D imaging of an acceptable quality. Additionally no methodhas been devised for transmission of 3-D images over conventionalbandwidths.

Three-Dimensional Imaging Techniques by Takanori Okoshi (1976) analyzesvirtually every 3-D imaging method ever devised to that date. Since thattime, most 3-D imaging technologies that have been developed use thetechnologies disclosed in Okoshi's book, and no radically new approacheshave been proposed. When discussing the prospects for 3-D television,Okoshi calculated that the bandwidth required to transmit aLenticular-Sheet 3-D Image, that is the lowest bandwidth required for anautostereoscopic 3-D picture, would be 750 MHz. This corresponds toabout 125 of today's conventional TV channels.

Okoshi's analysis shows that neither he nor anyone else knew how thebandwidth requirement could be reduced enough to transmit 3-D video, northat anyone could imagine what kind of display device could be devisedto show it. Okoshi predicted that the next generation of televisionbroadcasting would feature high-resolution, wide-screen display thatgave only an “illusion” of depth sensation. To support his prediction,Okoshi cited the beginning of an “epoch” in movies when Cinerama wasintroduced. Cinerama was a two-dimensional (2-D), curved, wide-screentechnique. According to Okoshi, the popularity of Cinerama resulted in adramatic decrease in efforts to develop other forms of 3-D.

The experience of 3-D is created in the presence of four conditions. Thefirst condition consists of what are collectively called 2-D cues. Thesecues mainly consist of objects getting smaller, higher, closer together,dimmer, less distinct, less contrasty and less colored as they getfurther away, as well of course as the fact that foreground objectsblock the view of background objects. These cues are recorded andreproduced in the course of standard 2-D image recording.

The second condition is parallax. Parallax occurs when a change ofposition of the viewer produces a different view in which backgroundobjects previously hidden by foreground objects become visible.Conventional 3-D stereo techniques lack an ability to convey parallax,but although parallax is not absolutely essential for a viewer toexperience 3-D, its presence adds a great deal of realism to 3-Dimaging.

The third condition is lateral binocular disparity. This means that thelateral (horizontal) relationship between at least two objects in thescene is different for each eye. This results in different amounts ofconvergence of the eyes to form a single perceived image of eachdifferent object in the scene. It can be reproduced by recording imagesof a scene from two (or more) different points of view.

The fourth condition is depth disparity, in which at least two objectsin the scene are not in focus to the eye at the same time. Thus,accommodation or re-focusing of the eye is required when moved from onesuch object to the other. This phenomenon, present in real life, is notreproduced with conventional 3-D imaging techniques. It requiresfocusing of at least two different components of a scene into at leasttwo different depth locations in space.

The inventor has found that this condition is very important because, asthe brain acts to refocus the eyes from one depth to the other, itexperiences the perception of true depth. Lack of the depth disparityphenomenon leads to eye strain and headaches after extended periods ofviewing in current 3-D imaging systems, because of the conflict betweenaccommodation and convergence. Preferably these four conditionscorrelate to one another when viewing a 3-D image so as to provide thesame relationships found when viewing a real life scene.

The popularity of Cinerama, as mentioned above, is especiallyinteresting because it was only a 2-D image projected on a very widecurved screen; yet it produced a realistic depth-containing experience.The effect indicates that something about the display was providing thebrain with depth information.

The depth cues present in a Cinerama display were very important andcompelling. First of all, a variety of 2-D depth cues were present. Asan object gets farther away, it gets smaller, higher up in the frame,less distinct, less color saturated, less contrasty and less bright.Object points get closer together as they recede, such as train tracksappearing to get closer together as they get further away, andforeground objects obscure background objects. Second, the objectsdepicted on screen were often small compared to the huge screen size.Third, the extremely wide screen necessitated that the viewers focustheir eyes differently, the process known as accommodation, when viewingobjects at the center of the screen as compared to when they viewedobjects on the sides of the screen. This effect was more pronounced thecloser one sat to the screen and the smaller each on-screen object was.If an object was nearly as big as the screen, the brain would reduce theviewer's perception of apparent depth. This is because different partsof such an object appeared at different depths, depending on where eachpart was on the wide screen. However, the brain knew that the entireobject should be at only one depth. This caused the brain to lose depthperception with regard to that object and just see it as a curved flatobject.

In real life, accommodation is an extremely important, but almostcompletely ignored, part of what causes depth perception. The eyesconstantly refocus on nearer and farther objects in a scene. Whenfocusing on objects at one distance, objects at another distance areseen as being out of focus, and the brain adjusts lens and cornealmuscles to bring into sharpest focus whatever one concentrates on. Dueto our eyes' limited depth of field, we can never get all objects (oreven all parts of any single three-dimensional object) into best focusat any one time. As we shift attention to blurrier objects in an attemptto sharpen their image for clearer recognition, we keep refocusing.Objects keep shifting from clear to blurry, creating a scene in constantflux made of a mix of sharper and blurrier images which keep changingtheir focus. This effect is even observable with one eye, creating thebasis for limited “monocular depth perception.”

While observing a scene, the brain also constantly shifts attention fromnearer objects to farther objects in the attempt to merge all perceiveddouble images. When viewing an object at a selected depth, the two eyesare aimed at that object so that the two views of that object overlapprecisely, creating a single image in the brain. This is calledconvergence. At the same time, other objects at other depths do not lineup and therefore appear to the brain as double images. As the brainconstantly shifts attention among nearer and farther objects, itexperiences a continuing flurry of single and doubled images. Throughlife experience, the brain forms a correlation between each degree ofaccommodation and each degree of convergence in response to viewingobjects at different depths.

In stereoscopy and autostereoscopy, as the object gets farther from theplane of the image, in front or behind, the convergence of the eyesincreases, but unlike reality, the accommodation stays the same (sinceall image information is in one plane). The farther away from the imageplane an object is, the larger is the discrepancy between accommodationand convergence. The discrepancy causes the brain to change theconvergence and accommodation of the eyes back and forth to create amatch between them based on past experience.

In such an experience, fatigue, eyestrain, and headaches result sincethe objects are, at least in part, not really in focus in the same planeas convergence makes them appear. Also, the further out of the plane ofbest focus the image appears due to convergence, the harder it is forthe viewer to see a 3-D image instead of a double image.

With Cinerama, although depth appeared limited, the appearance of depthwas striking because accommodation and convergence seemed to match whenlooking at different parts of the big screen, because the eyes had toboth converge differently and refocus.

This important component of three-dimensional perception (varyingaccommodation) is not reproduced in prior art 3-D imaging systems. Thisis because most 3-D imaging is done using stereoscopy orautostereoscopy. In stereoscopy, two images are recorded, onecorresponding to the left-eye view of the scene and the othercorresponding to the right-eye view. These two images are different,providing what is called “binocular disparity.” This difference forcesthe viewer's eyes to aim at objects at each selected depth to see themproperly. In stereoscopy, each eye is made to view only itscorresponding image through the use of an optical device such as red andgreen glasses, polarized glasses, or lenses which focus one image intoeach eye, such as in a stereoscope.

Autostereoscopy directs the corresponding images to the eye without theuse of any optical device near the person. Instead, optics are locatednear the images, restricting the angle of view of each image so thateach eye still sees only one of the two images. This has been done withlenses, prisms, and light-blocking barriers, for instance. Since theangle of view for each image can be made very narrow, many images can betaken from many angles and viewed one at a time as one moves one's head.This provides an aspect of 3-D perception, called motion parallax, notavailable from stereoscopy. With motion parallax, one can look aroundforeground objects to see previously hidden background objects. Theimages displayed using stereoscopy and autostereoscopy, however, are allin one plane, so the constant refocusing and perception of a mix ofsharp and blurry images—which the inventor has found to be so importantto the real 3-D experience—is absent. Due to this lack of variableaccommodation cues, stereoscopy and autostereoscopy present anotherdifference from reality that is significant.

When the two eyes receive different views of a scene, the brain overlapsthem, trying to line the images up exactly. However, two differentimages viewed from two different angles cannot line up exactly. Thisbinocular disparity gives the brain information about the depth of (ordistance to) an object being viewed. If one holds one's thumb in frontof some farther object, and focuses on the thumb with both eyes open,one will observe a double image of the farther object. A shift inattention to the farther object causes a double image of the thumb to beobserved.

As long as there are some changes in both convergence and accommodation,the viewer's brain perceives a scene as not flat. Once a scene isobserved to have depth, a variety of perspective cues complete theillusion of depth, and inform the viewer at what depth each objectappears to be.

SUMMARY OF THE INVENTION

An image display system provides a viewer with an experience ofthree-dimensional imagery by presenting a composite image made up of atleast two separate images. The system includes at least first and secondimage sources, a beam combiner, and a “background-image-occludingelement” which prevents background imagery from being seen throughforeground image elements. The system presents the image from one of theimage sources, containing background image information, at a distancefrom the viewer which is greater than the distance from the viewer tothe other image presented from the other image source, which containsforeground image elements. The “background-image-occluding element” ispositioned at the same optical distance from the viewer as the imagecontaining foreground image elements, eliminating any parallax errorbetween them, enabling the foreground image elements to always occludeappropriate areas of the background image, regardless of the viewer'sposition or the background image brightness relative to the brightnessof foreground image elements.

Also disclosed herein is a 3-D display system based on the inventor'srealization that an observer (interchangeably referred to herein as aviewer or player) experiences a perception of 3-D as seen in real lifewhen presented with as few as two planar images at different depths. Anadvantage is that the many of the embodiments disclosed herein presentsuch images at low cost and in a manner that is remarkably easy to use.Moreover video images in accordance with the present invention can betransmitted using significantly less bandwidth than convention 3-Dimaging techniques.

In one embodiment, the present display system employs an apparatus thatpresents two or more images in positions such that each of the images isspatially separated from each of the other images along a co-axialline-of-sight for a viewer (i.e. co-aligned). A viewer looking at theresulting display perceives a three-dimensional scene. The display ofthe present invention uniquely provides traditional 2-D cues, parallax,lateral binocular disparity and depth disparity, with unparalleledefficiency.

Many of the embodiments described herein provide (at least) a foregroundimage and a background image which are co-aligned, and employ at leastone optical element that acts as a beam combiner. The beam combiner isoptionally a reflective element such as a semi-silvered mirror or arefractive element such as a Fresnel beamsplitter (herein called aFresnel beam combiner because of the way it is used) or the Fresnelsemi-prism disclosed hereinbelow.

The foreground image and the background image are optionally generatedto display a foreground image plane that is imperceptible or at leasttransparent except where there are objects in the foreground imageplane. This quality of transparency allows objects on a background imageplane to be seen when the are not obscured by such foreground objects.However, the images are preferably related in a manner such that objectsin the background image are not perceptible through objects on theforeground image plane that are supposed to be opaque (by which theinventor means non-transmissive in the wavelengths of interest).Disclosed herein are various techniques and embodiments for theformation of such images for this display system.

Some versions of the image display apparatus employed in the presentinvention require the use of at least one lens which is used to create areal image (as distinguished from a virtual image) as part of thedisplay. Some versions present virtual images.

In a general form, the present invention provides an image displaysystem comprising a first image source, a second image source, and abeam combiner, wherein these elements are arranged so as to present to aviewer a foreground image from one of the image sources, and abackground image from the other of the image sources, the backgroundimage being presented at a greater distance from the viewer than theforeground image. In accordance with the invention, the viewer perceivesthe foreground image and the background image as part of a scene havingdepth. Generally the foreground image and background image areco-aligned to the line of sight of a viewer.

Optionally, when the first and second image sources are portions of acomposite image source (e.g. a television screen or monitor), such adisplay system also includes a reflective element disposed to reflectthe image of the second image source to the beam combiner. In that eventit is frequently desirable to provide an optical element between thebeam combiner and the viewer to modify the aspect ratio of theforeground image and the background image. Desirably the optical elementis a cylindrical mirror or a cylindrical lens.

Various embodiments of the present invention involve the use of ahousing which is adapted to be fastened to a conventional television setor monitor and which contains the optical elements of the presentinvention, the housing providing an aperture through which a viewerobserves the display. Such a system desirably comprises a housing and abeamcombiner within the housing, wherein the housing has a viewingaperture, a first image aperture, and a second image aperture; whereinthe first image aperture is adapted to a first image source; wherein thesecond image aperture is adapted to a second image source; wherein thefirst image aperture, the second image aperture, and the beamcombinerare so disposed as to present to a viewer through the viewing aperture aforeground image from one of the image sources, and a background imagefrom the other of the image sources, the background image beingpresented at a greater distance from the viewer than the foregroundimage.

It is a feature of preferred embodiments of the present invention toprovide means for minimizing bleed-through of the background images ontoa foreground image, wherein the foreground image appears translucent orghostly. Techniques disclosed herein include controlling relativebrightness of the two images, using a approach to dim out portions ofthe background image that are occluded by the foreground image. Toimprove the presentation of foreground objects by minimizing imagebleed-through, a mask is desirably interposed between the backgroundimage source and beamcombiner at a position that is the same distancefrom the beamcombiner as the foreground image source, so that the maskdisplays a silhouette of foreground objects that appear coincident withthe foreground image source, acting to mask portions of the backgroundimage from the viewer. The mask may be a light valve, e.g. an LCD.

In some embodiments a lens may be interposed between the first imagesource and the viewer so as to present at least one of the foregroundimage and the background image as a real image. The lens may be aFresnel lens or a lenserF lens as described hereinbelow. Desirably theyhave opaque rises as discussed below.

Some embodiments employ the optics of a conventional a projector, e.g. aslide or movie projector, to produce the 3-D effects of the presentinvention. A mirror is placed far enough out from the projector exitlens to divert portions of the projector's output to differentprojection screens. A portion of the beam is reflected to a projectionscreen. Another portion of the beam is caused to fall on a secondprojection screen, which may be disposed at a right angle from the firstprojection screen. Preferably, a lens is used to re-focus one of theportions, since the screens are at different distances from theprojector. Each portion reflects from its screen to a beamcombinerwhereby the portions are aligned. One portion is transmitted while theother portion is reflected in the same direction. Once the foregroundand background images are so aligned, they are redirected, refocusedinto real images, and optionally magnified, corrected for aspect ratio,for distortion, etc., as elsewhere taught in this document.

Another aspect of the present invention is a method for displayingimages to a viewer by simultaneously presenting to both eyes of a viewera first image that is generally planar, simultaneously presenting toboth eyes of a viewer a second image that is generally planar and isco-aligned with the first image along an axis that is in the generaldirection of the viewer but at a perceptibly different distance from theviewer than the first image, wherein the image that is at a distancecloser to the viewer depicts objects in the foreground of the displayedimages and the other of the images depicts objects in the background ofthe scene. A viewer observing the images perceives the depicted objectsas part of a scene having real depth.

The method desirably applies to moving images.

The method may be one wherein the first image and second image arepresented alternatingly to a viewer with a cycle that is within the timeframe of persistence of vision; or the first image and the second imagemay both be presented to the viewer simultaneously.

In many embodiments of this invention, the first image and second imageare each presented from an image source derived from a portion of thesame television screen.

In some embodiments, the displayed images are real images of first andsecond image sources. In others the displayed images are virtual imagesof first and second image sources. In yet others, the first image is areal image of a first image source and the second image is a virtualimage of a second image source.

In still others, the first image is a real image of a first image sourceand the second image is a second image source being viewed directly. Andin still others, the first image is a virtual image of a first imagesource and the second image is a second image source being vieweddirectly.

Exaggeration of traditional 2-D cues within the foreground image andbackground image can greatly increase the sensation of depth. Use oftraditional 3-D techniques, like stereoscopy, on the foreground andbackground image can also greatly increase the sensation of depth. Inaccordance with an aspect of the present invention, images are presentedusing any or all of the following enhancement techniques: exaggeratedperspective, enhanced difference in brightness between foreground andbackground objects, presentation of background objects higher in theframe than corresponding foreground objects. Also, the foreground imageplane, the background image plane, or both, are preferably tilted awayfrom the viewer to enhance depth perception. Another enhancementtechnique is accordance with the invention is to present an additionalfloor-plane image to the viewer.

In one embodiment, the present display system employs an apparatus thatpresents two or more images in positions such that each of the images isspatially separated from each of the other images along a co-axialline-of-sight for a viewer (e.g. co-aligned). A viewer looking at theresulting display sees data which has value when viewed simultaneously.Software and hardware of the present invention produce image data whichhas value when viewed simultaneously.

Various means for generating information about images are disclosed inaccordance with the present invention. For display on a TV screen ormonitor, each source image is divided into at least two image signals.These separate image signals produce separate images on differentportions of a single image display device, which are then opticallycombined to form a composite image scene or other display, or are usedto synchronously generate a plurality of images, each on a separatedisplay device, which are then optically combined to form the compositeimage scene or other display.

Image capture techniques may be employed in accordance with the presentinvention to capture live images. Using a first image capture techniquefor capturing images to be displayed using the present invention, afirst camera is directed at one or more foreground objects in a scene tobe captured. A second camera is positioned behind or above theforeground subject matter and directed at the scene to be captured.Techniques are presented to minimize or eliminate the backgroundinformation from the foreground image. Focus detection algorithms may beemployed to eliminate the out-of-focus subject matter from each image.

Two or three cameras horizontally displaced from one another, may beused: one to capture the scene from the left, one to capture the scenefrom the center, and one to capture the scene from the right. Theyprovide a composite full view of all background objects behind the oneor more foreground objects in the image.

Another multicamera technique comprises two horizontally-displacedcameras arranged in parallel fields of view at the same Z location.Matching objects from each image are recognized using computer matchingtechniques, and the distance from the image of each object to the edgesof the frame in each of the two images are calculated to determinedepth. At infinity, all objects overlap, but as objects get closer tothe cameras, the corresponding images become separated by greaterdistances.

Techniques as have been employed in colorization of motion pictures (inwhich the computer tracks a selected object or area from frame to frame)may be used to create the foreground image frame. Where real-timeprocessing is not an issue, foreground objects can alternatively beselected by hand. The same techniques can be used to produce abackground image devoid of foreground objects.

A single-camera technique of the present invention for identifyingforeground and background objects employs two lenses which are focusedon the same scene through a single aperture by way of a beamsplitter Onelens is focused on the foreground and the other is focused on thebackground, and each lens focuses an image on its own image detector.Using techniques which discard out-of-focus components, foreground andbackground objects are identified and eliminated from each of theforeground and background images as required. Fill techniques may beused to reconstruct background areas occluded by foreground objects.

One technique employs a camera whose sole purpose is to captureforeground objects. It is set for a narrow depth of field, and onlyin-focus objects are selected from the scene foreground. Anothertechnique to select foreground images in real time is to analyze thespatial frequency of the various portions of the image. Spatialfrequency is highest for in-focus objects. A spatial frequency thresholdis selected, and groups of pixels having a spatial frequency abovethreshold are determined to belong to foreground objects.

Contrast detection may be used for this purpose as well. Highestcontrast areas are generally found in foreground objects. Filteringtechniques are employed to look for the highest difference between darkand light areas of an image.

Because objects in the foreground of an image generally move morequickly than objects in the background, frame-to-frame motion detectiondiscriminates between foreground objects and background objects. Anothercharacteristic that can be used is color saturation, which decreases asobjects recede into the background. Others include brightness detection,since closer objects are usually brighter. Optical subtraction may beemployed with these techniques to eliminate portions of the image thatare the same in successive frames, resulting in an image of foregroundobjects. Different areas of the background will be blocked in successiveframes of the image. By storing the successive frames, the blockedbackground areas may be reconstructed by using selected background datafrom different frames.

Various ranging techniques may be employed during capture of liveimages, as disclosed hereinbelow. Another scanning technique applicableto the present invention is to scan the scene with a laser beam anddetect the reflection from objects in the scene. The reflected spot sizeis proportional to the distance traveled by the reflected beam. Anothertechnique employs a scanned laser beam that is pulsed for short periodsof time. The laser is configured to have a coherence length within whichall foreground objects reside. When the beam is reflected from an objectin the scene, the reflected beam is received and recombined with areference beam from the same laser, and an interference pattern willdevelop only for objects which reside within the coherence length. Adetector is used to detect the presence of the interference pattern.This technique identifies objects in the foreground. If the camera usedis scanning the scene in synchronization with the laser beam, each pixelin the scene can be identified as coming from a foreground object or abackground object by storing an additional bit with the pixel. Knownobject-detection techniques, such as analyzing pixels to find boundaries(large changes) which define the edges of an object, can be utilized tostore Z-coordinate information for entire objects rather than for eachindividual pixel, reducing the amount of Z-coordinate data that must bestored or transmitted for each frame.

In accordance with preferred embodiments of the invention, source imagesare divided into at least two images, at least one foreground image andat least one background image. Some techniques for dividing sourceimages are known and have been mentioned herein, while others are partof the present invention and have been disclosed herein. When bothforeground and background images are displayed on the same displaydevice, the computer or other device writing to the display device mustbe configured to write the foreground image to a first designated areaof the display device and to write the background image to a seconddesignated area of the display device. For example, if a raster-scannedCRT display is employed, the foreground image may be written to the tophalf of the CRT and the background image may be written to the bottomhalf of the CRT by supplying the pixel data for the foreground imageduring the first half of each display frame and supplying the pixel datafor the background image during the second half of each display frame.

If the plurality of divided images are formed on a single displaydevice, such as a CRT display, the present invention contemplatesemploying during viewing optical expansion of at least one of the imagesto recreate the aspect ratio of the original image. In the event thatoptical expansion techniques are employed, it is advantageous to displaythe image compressed in the direction which is to be expanded, e.g.,vertically. Such compression allows optical expansion without resultingin an image stretched in that direction.

Resolution enhancement steps may be performed on image data if the imageis to be optically expanded to restore aspect ratio. Pixel and lineinterpolating methods may be employed for this purpose.

The perception that a displayed object is undergoing Z-axis motion,i.e., receding into the background or proceeding into the foreground,may be enhanced according to the present invention by plane-switchingtechniques. Such techniques include the steps of gradually decreasingthe size of the object as it recedes in the Z direction and, at aselected time, moving the image of the object from the foreground imageto the background image. Likewise, objects in the background image whichare moving in the Z direction towards the viewer may be graduallyincreased in size and at a selected point are transferred from thebackground image to the foreground image. This effect may be implementedon a frame-by-frame basis using known image-processing techniques.

Some versions of the image display apparatus of the present inventionemploy relatively inexpensive lenses, preferably annular lensesdisclosed herein, that nevertheless avoid or minimize the objectionablecharacteristics of scatter, flare, chromatic aberration and sphericaldistortion that otherwise result from the use of lenses in such displaysystems. The improvement to optical elements having rises and faces(ones that are stepped, e.g. a Fresnel lens) disclosed herein employs alight-absorptive element adjacent the vertical rises so that the amountof light passing through or reflected from the rises is minimized.

Thus the present invention provides an improved optical element havingrise portions and face portions, wherein light transmitting through orreflected from the rise portions is substantially prevented from beingseen by an observer viewing an image formed by light passing through theannular lens. More particularly, the rise portions are coated with anopaque light-absorbent material.

The improved optical element may be a refractive optical element, inwhich event the rise portions are substantially opaque and the faceportions are substantially transparent. It may also have ananti-reflective coating. It may, for example, be a Fresnel lens or aFresnel semi-lens or a lenserF lens, as disclosed hereinbelow.

The improved optical element may be a reflective element, such as anannular mirror.

Various methods of making the improved optical element are part of thepresent invention. Such methods comprise the steps of producing anoptical element having rise portions and face portions, and imparting alight-absorbent coating to the rise portions. The optical element mayhave a series of annular grooves, or the grooves may be linear. Theelement may be refractive, in which event an antireflective coating mayalso be applied, or the element may be reflective.

The light-absorbent coating may be imparted to the rises by applyinglight-absorbing material to the element and selectively cleaning it soas to leave a coat of light-absorbing material adhering to the riseportions but not to the face portions. Adherence may be enhanced byroughening the rise portions in advance, such as by scratching, scoringor abrading.

Positive or negative photoresist may be used in the process in variousways. A coating of negative photoresist may be applied to the opticalelement so as to coat all faces and rises, then illuminating thephotoresist so that the rises are not illuminated, so that exposedphotoresist is only on the faces. Alternative, positive resist can beused, and only the rises illuminated. In either case, the element isthen developed to remove the photoresist from the rises, and opaquematerial that is capable of adhering to the rises is then applied to theelement. The photoresist is then removed from the faces by moredeveloping to dissolve away remaining resist together with any of theopaque material coated on it.

Alternatively a coating of negative photoresist may be similarly appliedto the optical element, then illuminating the photoresist so that thefaces are not illuminated, with exposed photoresist being only on therises. The element is then developed to remove the photoresist from therises, and opaque material that is capable of adhering to the rises isthen applied to the element. The photoresist is then removed from thefaces by developing to dissolve away exposed resist together with any ofthe opaque material remaining on it.

Alternatively, the photoresist itself may be dark colored or dyed andleft on the rises. Negative photoresist may be made to coat the risesselectively by exposing the rises but not the faces to light and thendeveloping the optical element to remove unexposed photoresist.Alternatively, dark positive photoresist may be made to coat the risesselectively by exposing the faces but not the rises to light and thendeveloping the optical element to remove exposed photoresist.

Other means for reducing flare and the like with stepped opticalelements that are disclosed herein are also within the presentinvention.

The present invention also contemplates use of a sandwich of opticalelements to provide a compact and lightweight adapter that can be placedin front of a television screen or monitor. The sandwich comprises aFresnel semi-lens of the present invention, which is aligned with aFresnel beam combining element. The Fresnel beam combining element ispreferably a commercially available Fresnel beamcombiner or a Fresnelsemi-prism of the present invention. The result is that the viewer seestwo co-aligned images, one at about the plane of the TV screen andanother that is a few inches behind it. If aspect-ratio correction isdesired, the image source is compressed on the TV screen and a Fresnelcylinder lens is disposed in front of the aforesaid sandwich.

Alternatively a holographic optical element may be constructed (usingknown techniques) with the equivalent functionality of the two or threesubelements of the Fresnel sandwich described herein to accomplish thesame tasks.

An embodiment of the present invention is a “narrow-profile” singleimage source display system. This embodiment uses numerous smallermirrors which decreases the distance the optical elements protrude fromthe image source. The display is split into numerous foreground andbackground areas. Each top portion is the foreground portion, and eachbottom is the background portion. Each set of portions is co-aligned.The resulting output is striped because no light passes directly fromany background portion. An optional lenticular expansion array is usedto expand each image set stripe so gaps or blank stripes are notpresented to the user.

A further aspect of the invention disclosed herein is a multiplayervideo game adapter. Such an embodiment allows two or more players toshare a single monitor and yet have mutually independent and “secret”3-D views of a computer screen or the like. Such a multi-player imagedisplay system would comprise two or more of the 3-D image displaysystems of this invention, wherein each image source (having aforeground and a background image) is a portion of an overall imagesource, e.g. a single monitor, and would further comprise means forreflecting each of the foreground and background images respectivelyfrom a specified one of the image sources to a specified one of theplayers.

An additional aspect of the multiplayer video adapter of the presentinvention is that a simplified version, presenting multiple 2-D images,may also be produced.

The techniques disclosed herein also include the fabrication of avirtual monitor of the present invention that minimizes glare that wouldotherwise reflect from the screen of a cathode ray tube (CRT), providesimproved security through controlled angle of view, and reduces exposureto radiation.

Additional advantages and features of the present invention will becomeapparent from the detailed description presented hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a 3-D imaging device of this invention.(Each of the 3-D imaging devices depicted herein is an embodiment of thepresent invention.)

FIG. 2 is a cross-section view of the embodiment represented in FIG. 1.

FIG. 3 is a view of a foreground image which consists of a person.

FIG. 4 is a view of a background image which consists of a house.

FIG. 5 is a “head-on” view of the foreground image of FIG. 3 and thebackground image of FIG. 4 displayed by a 3-D imaging device of thisinvention.

FIG. 6 is a perspective view of the foreground image of FIG. 3 and thebackground image of FIG. 4 displayed by a 3-D imaging device of theinvention.

FIG. 7 is a view of a foreground image which consists of white circleson a black surround.

FIG. 8 is a view of a background image, which consists of white squareson a hatched background.

FIG. 9 is a “head-on” view of the foreground image of FIG. 7 and thebackground image of FIG. 8 displayed by a 3-D imaging device of theinvention.

FIG. 10 is a perspective view of foreground image of FIG. 7 andbackground image of FIG. 8.

FIG. 11 is a head-on, wireframe view of foreground objects of FIG. 7 andthe background objects of FIG. 8.

FIG. 12 is a view of a foreground image which consists of two people.

FIG. 13 is a view of a background image which consists of a house and ashrub.

FIG. 14 is a perspective view of the foreground image of FIG. 12 and thebackground image of FIG. 13.

FIG. 15 is a “head-on” view of the foreground image of FIG. 12 and thebackground image of FIG. 13.

FIG. 16 is a view of a foreground image of two people.

FIG. 17 is a view of the foreground image in FIG. 16 which exaggeratesthe perspective cues in accordance with the invention.

FIG. 18 is a view of a foreground image and a background image.

FIG. 19 is a side view of foreground image and background image whereinthe background image is larger than the foreground image.

FIG. 20 is a side view of foreground image and background image whereinthe background image is tilted with its top away from the viewer.

FIG. 21 shows a foreground image which consists of a “smiley face” on ablack surround.

FIG. 22 shows a background image which consists of two square objects ona hashed surround.

FIG. 23 shows 3-D output as viewed head-on, or how a unified image mightlook if presented on a 2-D imaging device.

FIG. 24 shows the objects of foreground image of FIG. 21 as a wireframefrom a head-on perspective as they would occlude the background image ofFIG. 22 when displayed on a 3-D imaging device.

FIG. 25 shows a head-on perspective of the output of a light valve orLCD as it occludes the background image of FIG. 22.

FIG. 26 is a cross-section view of an embodiment showing the placementof an LCD or silhouette so its output properly masks the backgroundbehind foreground objects.

FIG. 27 is a cross-section view of a 3-D imaging device which utilizesportions of a single image source to create foreground and backgroundimages.

FIG. 27A is a cross-section view of the embodiment of FIG. 27 whichshows the housing in alternate positions.

FIG. 28 is a cross-section view of a 3-D imaging device of thisinvention illustrating potential problems with a user having a directline-of-sight to the image source.

FIG. 29 is a cross-section view of a 3-D imaging device of the inventionwhich avoids the line-of-sight problem presented in some otherembodiments.

FIG. 30 is a cross-section view of a 3-D imaging device of the inventionwhich has secondary optics to further change the path of light to aviewer.

FIG. 31 is a perspective view of an image source, a Fresnel lens, andthe real image of the image source.

FIG. 32 is a side view of an image source, a Fresnel lens, the realimage of the image source, and the angle of view in which the real imageis perceived.

FIG. 32A is a perspective view of a faceted Fresnel lens.

FIG. 32B is a plan view of the faceted Fresnel lens in FIG. 32A.

FIG. 33 is a cross-section view of a 3-D imaging system which uses aFresnel lens.

FIG. 34 is a plan view of a 3-D imaging system of the present inventionwhich uses a Fresnel lens.

FIG. 34A is a plan view of a 3-D imaging system of the presentinvention.

FIG. 34B is a plan view of a 3-D imaging system of the presentinvention.

FIG. 34C is a plan view of a 3-D imaging system of the presentinvention.

FIG. 35A is an elevation view of a Fresnel lens.

FIG. 35B is a cross-section view of a Fresnel lens taken at line35B-35B.

FIG. 36 is a cross-section view of a “lenserF” lens (LenserF is Fresnelbackwards).

FIG. 37 is a cross-section view of a plano-convex lenserF lens.

FIG. 38 is a cross-section view of a portion of a Fresnel lensschematically illustrating light passing through the rise portion of thelens.

FIG. 39 is a cross-section view of a portion of a Fresnel lens which hasa scored rise and shows light reflecting and scattering from the scoredrise.

FIG. 40 is a cross-section view of a portion of a Fresnel lens which hasan opaque coating on the rise, reducing scatter and flare.

FIG. 41 is a plan view of an annular lens of the present invention whichis coated with photoresist and is partially covered with a light shield.

FIG. 42 is a cross-sectional elevation view of the annular lens of FIG.41, taken along the line 48-48.

FIG. 43 is a cross-section view of a sheet of plastic lens materialhaving opaque pre-printed rings thereon, preparatory to being formedinto an annular lens of the present invention.

FIG. 44 is a cross-section view of a step in the formation of an annularlens of the present invention by a press or mold, forming a lens withopaque rises from the sheet of plastic material shown in FIG. 43.

FIG. 45 is a cross-section view of a portion of an annular lens, and awave plate, schematically illustrating the passage of beams of polarizedlight therethrough.

FIG. 46 is a cross-section view of a portion of an annular lens coatedwith anti-reflective (AR) coating, schematically illustrating the effectof AR coating on a beam of light.

FIG. 46A is a plan view of an optical element of the present invention.

FIG. 46B is a perspective view of two optical elements of the presentinvention.

FIG. 46C is a plan view of an optical element of the present invention.

FIG. 46D is a perspective view of two optical elements of the presentinvention.

FIG. 47 is a view of an image source.

FIG. 47A is a plan view of a 3-D imaging system of this invention.

FIG. 48 is a perspective view of the 3-D imaging system of FIG. 47.

FIG. 49 is a plan view of an imaging system which functions as amultiplayer adapter.

FIG. 49A is a perspective view of the imaging system of FIG. 49.

FIG. 50 is a view of an image source of the present invention.

FIG. 51 is a plan view of a multiplayer 3-D imaging system of thisinvention.

FIG. 52 is a perspective view of the embodiment in FIG. 51.

FIG. 53 is a plan view of another embodiment of the multiplayer 3-Dimaging system of this invention.

FIG. 54 is a perspective view of the embodiment in FIG. 53.

FIG. 55 is a plan view of yet another embodiment of the multiplayer 3-Dimaging system of this invention.

FIG. 56 is a perspective view of the embodiment in FIG. 55.

FIG. 56A is a plan view of yet another embodiment of the multiplayer 3-Dimaging system of this invention.

FIG. 56B is a perspective view of the embodiment in FIG. 56A.

FIG. 57 is a plan view of another multiplayer 3-D imaging system of thisinvention.

FIG. 58 is a plan view of another multiplayer 3-D imaging system of thisinvention.

FIG. 59 is a plan view of another multiplayer 3-D imaging system of thisinvention.

FIG. 60 is a plan view of another multiplayer 3-D imaging system of thisinvention.

FIG. 61 is a plan view of another multiplayer 3-D imaging system of thisinvention.

FIG. 62 is a plan view of another multiplayer 3-D imaging system of thisinvention.

FIG. 63 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 64 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 65 is a perspective view of another multiplayer imaging system ofthis invention.

FIG. 66 is a plan view of the multiplayer imaging system of FIG. 65.

FIG. 67 is a view of an image source.

FIG. 68 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 69 is a perspective view of the multiplayer imaging system in FIG.68.

FIG. 70 is a view of an image source.

FIG. 71 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 72 is a perspective view of another multiplayer imaging system ofthis invention.

FIG. 73 is a plan view of the multiplayer imaging system of FIG. 72.

FIG. 74 is a view of an image source.

FIG. 75 is a plan view of an imaging system of this invention.

FIG. 76 is a perspective view of the imaging system of FIG. 75.

FIG. 77 is a plan view of an imaging system of this invention.

FIG. 78 is a perspective view of the imaging system of FIG. 77.

FIG. 79 is a perspective view of the image source and a conventionalmirror.

FIG. 79A is a perspective view of the image source and a conventionalmirror.

FIG. 80 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 81 is a perspective view the multiplayer imaging system of thisinvention.

FIG. 82 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 83 is a perspective view the multiplayer imaging system of thisinvention.

FIG. 84 is a plan view of another multiplayer imaging system of thisinvention.

FIG. 84A is a diagrammatic view of a display system of this invention.

FIG. 85 is an elevation view of a monitor enlarger imaging system ofthis invention.

FIG. 86 is an elevation view of a monitor enlarger imaging system ofthis invention.

FIG. 87 is an elevation view of an image display system of thisinvention.

FIG. 88 is a plan view of the image display system of FIG. 87.

FIG. 89 is a side view of an image display system of the presentinvention.

FIG. 90 is a side view of an image display system of the presentinvention.

FIG. 91 is a side view of an image display system of the presentinvention.

FIG. 92 is a side view of an image display system of the presentinvention.

FIG. 100A is a side view of an image display system of the presentinvention.

FIG. 100B is a perspective view of an image display system of thepresent invention.

FIG. 100C is a perspective view of an image display system of thepresent invention.

FIG. 100D is a perspective view of an image display system of thepresent invention.

FIG. 100E is a perspective view of an image display system of thepresent invention.

FIG. 101A is a plan view of an image display system of the presentinvention.

FIG. 101B is a plan view of an image display system of the presentinvention.

FIG. 102A is a perspective view of an image display system of thepresent invention.

FIG. 102B is a perspective view of an image display system of thepresent invention.

DETAILED DESCRIPTION

Real-Depth 3-D Imaging

The present invention provides what may be termed real-depth imaging,since there are real differences in depth between images of objects in ascene. In accordance with the invention, different objects at differentdepths in a scene are presented in different planes in space, one behindthe other. The object areas of each plane are perceived as opaque, andthe non-object areas are clear to allow observation of the images inmore distant planes.

The inventor's experimentation revealed that images created in only twoplanes provide a satisfactory real-depth experience. The inventor'sdiscovery that only two images, projected in different planes, areneeded to achieve a 3-D experience greatly simplifies from those of theprior art, the system necessary to produce such images. Moreover, theinformation content (i.e. the bandwidth) necessary to transmit suchimages is at a level which can be readily transmitted via a conventionalTV channel or over the Internet. This discovery provides a solution tothe previously mentioned dilemma that had been identified by Okoshi.

However, it is also within the scope of the present invention to utilizemore than two planes, when desired to achieve even greater realism in aresulting display.

In designing and fabricating embodiments of the present invention, thoseskilled in the art of optical displays have reference to numerous booksand catalogs which embody the conventional teachings and provideinformation about commercial sources of optical elements and supplies,and for conciseness of presentation need not be repeated in detail here.By way of example, a four-volume reference work collectively entitledThe Photonics Directory (42nd International Edition 1996) is availablein print and on CD ROM from Laurin Publishing Co., Inc. (Pittsfield,Mass. Photonics@MCIMail.com). Various suppliers of optical elementspublish catalogs which not only identify their products but alsohelpfully summarize how to use them, for example Rolyn Optics Company(Covina, Calif.) Catalog 195; Oriel Corporation (Stratford, Conn.) ThreeVolume Catalog; Edmund Scientific (Barrington, N.J.) 1996-1997 Opticsand Optical Instruments Catalog. These publications and all otherreferences mentioned in this document are hereby incorporated byreference.

In a first embodiment of the invention, a foreground image is formed ona first plane and a background image is formed on a plane located moredistantly from the observer. The images are generally co-axial from thevantage point of the observer. The foreground image presents selectedobjects on a black surround. This black area appears as a blank ortransparent space through which the background image is seen.

FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 is aperspective view thereof. FIG. 2 shows a cross-sectional view of thehousing 1-001. The housing 1-001 has a front face 1-002, a left face1-003, a top face 1-004, a rear face 1-005, and a bottom face 1-006. Thehousing 1-001 has on its front face 1-002 a viewing aperture 1-012through which a viewer 1-200 (diagrammatically represented as a stylizedeye, although it is to be understood that both eyes of the viewer aretypically open) can perceive a 3-D scene.

The housing 1-001 has on its rear face 1-005 a foreground aperture1-014. The housing 1-001 has on its bottom face 1-006 a backgroundaperture 1-016.

Disposed within the housing 1-001 is an optical element 1-035, such as apartially reflective (e.g. semi-silvered) mirror. In use, the foregroundaperture 1-014 is positioned to permit light from a foreground imagesource 1-040 (e.g. a TV monitor) to pass into the housing. A foregroundimage 1-050 is shown on the foreground image source 1-040. Theforeground image 1-050 is seen directly by the viewer (i.e. withoutreflection) through the partially reflective optical element 1-035. Inuse, the background aperture 1-016 is positioned to permit light from abackground image source 1-080 (e.g. another TV monitor) to pass into thehousing. A virtual background image 1-090 appears displaced behind theforeground image 1-050.

For illustrative purposes, FIG. 1 shows a first light ray 1-100 and asecond light ray 1-101. The first light ray 1-100 passes from theforeground image source 1-040 through the foreground aperture 1-014,directly through the partially reflective optical element 1-035, andthen through the viewing aperture 1-012 to a viewer 1-200. (Not shown isthat some of the light from the foreground image 1-050 is reflectedupwards within the housing by the optical element 1-035, since it issemi-reflective. The interior of the housing is light-absorbent, e.g.painted black or covered with black velvet, to prevent such stray lightfrom interfering with the intended images.)

The illustrated second light ray 1-101 passes from the background imagesource 1-050 through the background aperture 1-016 to thesemi-reflective optical element 1-035. The second light ray 1-101 isthen reflected from the semi-reflective optical element 1-035 throughthe viewing aperture 1-012 to a viewer 1-200. Light (such as isrepresented by the second light ray 1-101) which comes from thebackground image source 1-050 is perceived by the viewer 1-200 as comingfrom the location of the virtual background image 1-090, even though itis in fact coming from the background image source 1-080. Note that thedistance from the background image source 1-080 to the middle of theoptical element 1-035 is the same as the distance from the virtualbackground image 1-090 to the same point on the optical element 1-035.

The aforesaid optical element 1-035 acts as a beamcombiner, aligning theforeground image 1-050 and the virtual background image 1-090. Some ofthe light 1-102 and 1-103 reflected or transmitted is misdirected inthis embodiment by optical element 1-035 and is absorbed within thehousing 1-004. A viewer 1-200 looking at the foreground image 1-050 andthe virtual background image 1-090 will perceive both images as beingco-axial along the same line-of-sight, but at different distances fromthe viewer 1-200. Objects located on foreground image 1-050 arephysically closer to the viewer 1-200 than objects on the virtualbackground image 1-090.

Because the foreground image 1-050 and the virtual background image1-090 are in different locations in space, a viewer 1-200 who bobs herhead will notice parallax between the foreground image 1-050 and thevirtual background image 1-090. In accordance with the inventor'sdiscovery, the inventor has found that the typical viewer tends toperceive a foreground image and background image formed this way asparts of an overall scene having real depth.

The foreground image is presented in greater brightness than thebackground image. Hence the foreground image appears solid, appearing toobscure or block the background image as it would if it really weresolid.

Note that when the source of the foreground image is a transparency heldin place before a background image, the blank surround is desirably leftclear at printing. The surround is desirably blank when the foregroundimage is a light valve held in place before a background image, or whenmultiple light valves are held in series to create multiplanar effects.

In the case of other image sources, like a CRT or a photograph, theblank surround is desirably black, so as not to interfere with theviewer's perception of the background image.

Image sources, as contemplated by the present document, are any sourceof imagery, such as CRT's, plasma displays, stereographic 3-D images,television monitors, LCD's, transparencies, photographs, illuminatedobjects, flat or curved front or rear-projection screens on which imagesare projected, or any portion thereof.

In accordance with the present invention, a scene to be viewed ispreferably divided into at least two images, presented on two co-axialplanes. Two-dimensional cues, including perspective and backgroundobject occlusion, are provided in each plane. A viewer observing theimages continually shifts attention from plane to plane, simultaneouslychanging accommodation and convergence. As in real life, a scenepresented by the 3-D display system of the present invention appears tobe a mix of sharper and blurrier images and single and doubled imageswhich keep shifting. If the viewer moves or shifts position, bothhorizontal and vertical parallax are perceived. At all times, in allviewing positions, the two eyes of an observer see different perspectiveviews, creating binocular disparity that further stimulates the braininto perceiving a real-life depth experience. Surprisingly, a scenedisplayed this way with perspective cues appears to have continuousdepth and not to be confined to only two planes, regardless of whethersuch a scene is moving or still.

FIG. 3 shows an illustrative foreground image 3-050. On the foregroundimage 3-050 is a black surround 3-052 on which there is a foregroundobject 3-054, a person. FIG. 4 is a background image 3-090. On thebackground image there is a background object 3-094, a house. FIG. 5 isa “head on” perspective view of the foreground image 3-050 and thebackground image 3-090. The foreground object 3-054 partially occludesthe background object 3-094. FIG. 6 is a different perspective view ofthe foreground image 3-050 and the background image 3-090. In FIG. 6,the foreground object 3-054 partially occludes a different portion ofthe background object 3-094 than it does in FIG. 5.

The foreground image 3-050 and the background image 3-090 appear indifferent planes. The foreground image 3-050 has a foreground object3-054 or multiple foreground objects on a black surround 3-052. Theblack surround acts as a transparent space through which the backgroundimage 3-094 can be seen. The foreground object 3-054 will appear solidif it is of sufficient brightness with regard to the background image3-090 and any background object 3-094.

As noted previously, the experience of 3-D is created in the presence offour conditions: traditional 2-D cues, parallax, lateral binoculardisparity, and depth disparity. Traditional 2-D cues are present in thisembodiment: the background object 3-094 is higher up in the frame,smaller, and less contrasty than the foreground object 3-054. There isparallax, as a change in the position of the viewer, as seen in FIGS. 5and 6, produces a different view in which portions of a backgroundobject 3-094 previously hidden by foreground object 3-054 becomevisible. There is depth disparity as only one of the foreground object3-054 or the background object 3-094 is in focus for a viewer at any onetime.

If the foreground image 3-050 and background image 3-090 were displayedusing the embodiment shown in FIGS. 1 and 2, a viewer 1-200 who bobbedher head from side to side or up and down would see the parallax changeindicated in comparing FIG. 5 with FIG. 6. It was surprising that thissimple embodiment can create such a true feeling of depth. The inventorfirst thought that more than two planes would be required to create asensation of continuous depth, but it turns out that two planes aresufficient.

Problem areas occur when a foreground object is aligned with abackground object. The foreground object may appear ghostly orinsubstantial if the background object is visible through it. It isdesirable to make the foreground image brighter than the backgroundimage source to avoid such bleedthrough of objects.

One way is to make the foreground image source brighter (i.e. byincreasing the brightness of the foreground image). In some embodiments,it is possible to ensure that the background image is dimmed to thedesired extent by the beamcombiner (e.g. reflector or refractor) used toco-align foreground and background images.

Another method to minimize bleedthrough involves dimming the backgroundimmediately behind the foreground objects. Of course, with parallax, itis difficult to ascertain what is “behind” a given foreground object,since that changes from viewpoint to viewpoint, and even from eye to eyeof a (two-eyed) viewer. A solution to this difficulty is to dim an areaon the background that is slightly larger than the foreground object. Insome applications, this sort of “flying spot” shadow is desirable,whereas in others it would be distracting to the presentation. Theshadow is preferably tapered so it is darkest in its center and lightenstoward the edges so no hard boundary is created.

FIGS. 7 through 11 illustrate a potential problem with imagebleed-through. FIG. 7 is a foreground image 7-050. On the black surround7-052 on the foreground image 7-050 is a first foreground object 7-054and a second foreground object 7-055.

FIG. 8 is a background image 7-090. On the striped surround 7-092 on thebackground image 7-090 is a first background object 7-094 and a secondbackground object 7-095. FIG. 9 shows a “head on” perspective view ofthe co-aligned foreground image 7-050 and the background image 7-090.Note that first foreground object 7-054 partially occludes the stripedsurround 7-092 and also partially occludes the first background object7-094. FIG. 10 is a view from a slightly different perspective of theforeground image 7-050 and background image 7-090. Note that, incomparison with FIG. 9, different portions of the striped surround 7-092are occluded by the first foreground object 7-054 in the view of FIG.10.

FIG. 11 illustrates a potential problem area 11-116 that may arise whenforeground image 7-050 and background image 7-090 are viewed from a“head-on” perspective. Light from the first background object 7-094 maybleed through the first foreground object 7-054, giving the firstforeground object 7-054 a ghostly or insubstantial appearance, damagingthe perception of a 3-D scene.

In the context of an embodiment as in FIGS. 1 and 2, the inventor foundthat when the foreground image 2-050 is brighter than the virtualbackground image 2-090, it helps to eliminate this ghostly orbleed-through problem. The foreground image 2-050 can be made brighterthan the background image 2-090 in various ways. One way is throughselection of a reflective element 2-035 which reflects less of the lightfrom the background image 2-090. Another method is to ensure that theforeground image source 2-040 is at least twice as bright as thebackground image source 2-080. Other methods as known in the art can beused to control the relative brightness of the final images.

FIGS. 12 through 15 show a different foreground image 12-050 andbackground image 12-090. FIG. 12 is a foreground image 12-050. On it area first foreground object 12-054 and a second foreground object 12-055.FIG. 13 is a background image 12-090. On it are a first backgroundobject 12-094 and a second background object 12-095. FIG. 14 is aslightly “off-line” perspective view of the foreground image 12-050 andthe background image 12-090. FIG. 15 is a “head on” perspective view ofthe foreground image 12-050 and the background image 12-090.

The inventor has found that the addition of traditional 2-D cues withinthe foreground image 12-050 and the background image 12-090 greatlyincreases the perception of 3-D. Note that first foreground object12-054 partially occludes second foreground object 12-055. The secondforeground object 12-055 is higher in the frame, smaller, etc. than thefirst foreground object 12-054. Similar effects happen in the backgroundimage 12-090. In addition to what is shown in the drawing, it can bemade to have less contrast.

Exaggeration of traditional 2-D cues within the foreground image andbackground image can greatly increase the sensation of depth. FIG. 16shows foreground image 12-050. FIG. 17 shows a modified foreground image17-050, on which are a first foreground object 17-054 and a secondforeground object 17-055. The perspective cues in foreground image17-050 have been exaggerated: the second foreground object 17-055 hasbeen made much smaller than the first foreground object 17-054.Similarly, the second foreground object 17-055 is higher in the frame,more dim, etc.

Creation of a sensation of depth is further enhanced when the foregroundimage is smaller than the background image. FIG. 18 shows a foregroundimage 18-050 and a background image 18-090. FIG. 19 shows the foregroundimage 18-050 and the background image 18-090 as seen by a viewer 19-200.If the foreground image 18-050 is smaller than the background image18-090, the images will appear properly proportioned when looked at by aviewer 19-200 since the background image 18-090 is farther away from theviewer than the foreground image 18-050. The background image 18-090 canbe made larger by using a larger background image source. Alternatively,intervening magnifying optics are employed to expand the backgroundimage 18-090.

FIG. 20 shows a viewer 20-200, a foreground image 20-050 and abackground image 20-090. A sensation of continuous depth can be enhancedby tilting either the foreground image 20-050, the background image20-090, or both, away from the viewer. As a viewer 20-200 looks higherin the frame, the objects are actually farther away from the viewer thanobjects which are lower in the frame, contributing to a perception of acontinuous depth scene. Although it is preferable to tilt the backgroundimage plane as a method to enhance connectedness between the planes, athird “floor-plane” image is optionally created with another imagesource, such as a CRT, being placed along the “floor” between theforeground image and the background image.

Use of stereographic and other “3-D” imaging techniques of the prior artas images for display systems and methods of the present invention canalso greatly enhance the perception of 3-D.

Another method for solving the bleedthrough problem involves the use ofa light valve. The light valve is placed between the background imagesource and any beamcombiner used to make the images co-axial. The lightvalve is placed the same distance from the beamcombiner as is theforeground image source. In the simplest embodiment, the light valve isa binary liquid crystal display (LCD) which is made black whereverforeground objects exist and is transparent otherwise. In this manner,no stray light passes from the background through the foreground object.There is parallax between the foreground image and the background image,which is tracked by the parallax between the light valve and thebackground image. A user who moves her head will see appropriatebackground around foreground objects, but not through them.

Such an embodiment of this invention will assist in making many sorts offoreground images appear to be very substantial. Take the example of aforeground object in which blackness is a feature. If any light from thebackground bleeds through the area that is supposed to be black, thatobject will appear ghostly and insubstantial. For example, where aforeground object is a person wearing a black tie and the backgroundimage is a roaring fire, seeing the fire through the tie would be anundesired effect.

FIG. 21 is a foreground image 21-050. FIG. 21 has a black surround21-052 on which is a foreground object 21-054. Foreground object 21-054has a first eye 21-055 and a second eye 21-056. The first eye 21-055 andthe second eye 21-056 are black areas where blackness is a feature ofthat area. The first eye 21-055 and the second eye 21-056 are meant tobe opaque, in contrast with the black surround 21-052 which is black soas to allow perception of a background image.

FIG. 22 is background image 21-090. Background image 21-090 has astriped surround 21-092, and a first background object 21-094 and asecond background object 21-095. FIG. 23 is a “head-on” perspective viewof the foreground image 21-050 and the background image 21-090, whichhave been co-aligned using a device of the present invention. FIG. 24 isalso a “head-on” perspective view of the co-aligned foreground image21-050 and the background image 21-090, with the foreground image 21-050rendered as a transparent wireframe so as to define a problem area24-114.

A problem area 24-114 results when a viewer has line-of-sight through ablack object which is supposed to be opaque to a portion of thebackground image which is light colored. In this case light frombackground object 21-094 is in line with the first eye 21-055.Unimpeded, this light would give the first eye 21-055 a ghostlyappearance. The first eye 21-055 would appear transparent, not black.Increasing the brightness of the foreground image 21-050 does not solvethis type of bleed-through problem, as multiplying the brightness ofblack (namely, zero) by a factor results in zero, and thus still black.

One potential solution is to dim the portion of the background image21-090 that is behind foreground objects like first eye 21-055.Depending on the position of the viewer 2-200, different portions of thebackground image 21-090 are behind foreground objects. Parallax makesareas like problem area 24-114 a moving target. A dimmed “head-on”problem area 24-114 is perceived by a viewer 2-200 looking around aforeground object 22-052 to the background 23-090. Using “flying spot”technology on the background 23-090 to solve the “head-on” problem areasis potentially damaging to realistic parallax.

A solution to the “flying spot” or masking problem is to employ anelement which stops the background image 23-090 from interfering withthe foreground image 22-050: a light valve 25-115 (or, in the case of astill picture, a silhouette will do) that is opaque wherever there areforeground objects. Using a light valve in this fashion will allowforeground objects which have blackness as a feature to occludebackground objects. FIG. 25 depicts a silhouette that could be used tomask the problem area 24-114 discussed in connection with FIGS. 21through 25.

FIG. 26 shows one embodiment of the present invention that uses such alight valve. Disposed within the housing 26-001 is a light valve 26-115.Also within the housing 26-001 is a reflective element 26-035, such as apartially reflective mirror. Disposed near the foreground aperture26-014 is a foreground image source 26-040. A foreground image 26-050 isshown on the foreground image source 26-040. Near the backgroundaperture 26-016 is a background image source 26-080. A virtualbackground image 26-090 appears, displaced behind the foreground image26-050.

The light valve 26-115 is placed between the reflective element 26-035and the background image source 26-080. The light valve is placed at thesame distance from the reflective element 26-035 as the foreground image26-050 on the foreground image source 26-040 (as indicated with arrows26-100). In this manner, a virtual light valve is created which iscoincident with the foreground image 26-050.

There is parallax between the foreground image 26-050 and the backgroundimage 26-090, which is tracked by the parallax between the light valve26-115 and the background image 26-090. Any inappropriate light from thebackground image source 26-080 is blocked by the light valve 26-115,giving the desired effect without any of the complex problems ofbackground object masking or background object fading. A simple binarylight valve is the preferred embodiment for simplicity and lowerexpense.

Referring once again to FIG. 24, the first eye 21-055 would be perceivedas black, while retaining its ability to occlude the background image21-090. The black surround 21-052 would remain transparent so thebackground image 21-090 can be viewed around foreground object 21-054.

Some processing of the images, either manual (as is done in cartooning)or automatic (using for instance the sort of software that is used incolorizing movies) may be necessary in order to generate appropriateoutput for the light valve. In the case of computer-generated content(like a video game or a movie consisting entirely of computer-generatedcontent like Toy Story or a television show consisting largely ofcomputer-generated content like Reboot or Transformers Beast Wars CGseries) a signal which is sufficiently sophisticated to drive the lightvalve of this embodiment may be readily provided as a byproduct of thecomputer-generation process.

By “sophisticated,” the inventor means that it is capable of dealingwith the particular combination of foreground image and background imagebeing presented so as to provide realistic object occlusion. Consider asan example: in the foreground, a man wearing a black tie (i.e., objectwhere blackness is a feature) holding at arm's length a donut that isoriented so the viewer has line-of-sight to the background (i.e., objectwhere blackness is meant to be a transparency). For the backgroundimage, once again, a raging fire. A sophisticated object definitionwould allow light from the fire (the background object) to pass throughthe hole of the doughnut without passing through the man's black tie. Insuch a sophisticated representation of the image, the hole is not partof the donut, but is instead considered part of the blank surroundthrough which the background is seen.

Additional discussion regarding the type and amount of depth informationwhich is preferably captured (either at recording or on the fly throughcomputer-aided image processing) is provided hereinbelow.

Most of the embodiments of the present invention preferably contain oneor more optical elements in a housing. The housing contains one or moreimage sources, or alternatively it may be provided with one or moreapertures through which light from an external image source passes. Thehousing is optionally designed to contain at least one image sourcewhile having an aperture for receiving light from at least one otherimage source. The housing preferably has an interior of light-absorbentmaterial so any stray light which hits it is not reflectedinappropriately (i.e. to the viewer directly or indirectly).

The housing preferably has a viewing aperture, through which the viewerperceives the images. The viewing aperture is preferably smaller thanthe image source, e.g. when a larger viewing aperture wouldimpermissibly allow a viewer to have a potentially detracting directline-of-sight to a background image source.

The housing is optionally designed so it can be easily placed on or nearan image source and easily removed from being near an image source. Forexample, some embodiments for television sets and computer monitors areequipped with hinges or Velcro fastening tape so they can be flippedfrom being in front of the monitor to a storage position on top of themonitor.

The housing is optionally designed so an image source can easily beremoved from being near it. A housing is potentially collapsible, tofacilitate storage or portage of the unit. An adapter which uses a stillpicture as a background image, for example, can be made so the stillpicture is easily removed from the adapter. Similarly, an embodimentwhich is used as a demonstration unit or a portable advertising unit ispreferably provided with a holding element which allows an image sourcesuch as standard LCD projector to be mounted on or in the housing.

The housing is often proportioned to the image source. Housings havebeen made for very small embodiments (image source having a diagonalmeasured in a fraction of an inch) and very large embodiments (imagesource having a diagonal of a few yards). Use in hand-held viewers,personal televisions mounted in head-gear, conventional television andcomputer monitors, projection units, and billboard size advertisingdisplays are some of the contemplated embodiments of this inventionillustrating part of the range of sizes contemplated for this invention.

Some embodiments of the display adapter invention use a single unifiedimage source as the original source of at least the foreground image andthe background image. For example, some embodiments use a singlestandard television or computer monitor as an image source. One portionof the screen is used for the foreground image and another portion isused to provide a background image. In some embodiments a mirror is usedas a means to reflect light from the background image source to aco-aligning, or beamcombining, element.

In those embodiments using conventional reflective optics (e.g. a planarmirror) it is also contemplated to employ alternatively a magnifyingreflective optic, such as a spherical mirror or Fresnel mirror, where alarger image is desired. Conversely a minifying reflective optic isoptionally employed where a smaller image is desired.

As an example of the display adapter of this invention with a singleimage source, where the bottom half of a television screen is thebackground image source and the top half of it is the foreground imagesource, the background image is optionally reflected by a mirror to thebeamcombining element. In fact, in one embodiment discussed hereinbelow,a lens sandwich assembly is provided, which acts to co-align the imageswithout any additional reflective optics being necessary to reflectlight from the background image source.

These “split screen” embodiments can suffer from small size and adistortion of aspect ratio. A halved television screen is either“landscape” if cut horizontally or “portrait” if cut vertically. For ahalved screen, a 2:1 image compression can be used in conjunction withoptics designed to uncompress the image. Such optics would includecylindrical optical elements to uncompress an image in a singledirection. Cylindrical mirrors or cylindrical Fresnel lenses arerelatively cheap to manufacture, and they can be used in pairs whereuniform expansion of an entire image is desired.

Of course there are many times when it is not desirable to halve thescreen even though it is split. For example, in some embodiments alarger background image source is called for so it will appear properlyproportioned to the foreground image source. The background image, ifnot made larger, can appear too small for its foreground image since thebackground image is actually farther away from the viewer than theforeground image as discussed hereinabove.

Single Image Source for 3-D

By using a single image source for providing both the foreground imageand the background image, a real-depth experience is optionally providedat moderate cost to the user, avoiding the expense of multiple imagesources such as when each additional image source is a computer monitoror a television set. In one such method, an image source, such as atelevision or computer monitor screen, is split in portions. One portionis used to generate each plane. For example, one portion of the screenis used to generate a foreground image, and another portion is used togenerate a background image. The background image is often reflectedninety degrees through the use of a mirror. Once that has beenaccomplished, foreground image and background image are optionallyco-aligned as elsewhere taught in this document (i.e. through an elementsuch as a beamcombiner). Once again, the inventor was surprised at thepronounced 3-D effect created through the use of the present invention,especially on foreground and background images generated from a singleimage source.

As mentioned elsewhere herein, it is desirable to present images whichare farther from a viewer, (such as a background image) as larger thanimages which are closer to a viewer, (such as a foreground image). Whena single image source is subdivided, for example, a larger portion ofthe image source may be used for the background image to compensate.Alternatively, magnification is used to enlarge the background image astaught elsewhere herein.

FIG. 27 shows an embodiment of the present invention. Housing 27-001 hasa front face 27-002, a top face 27-004, a rear face 27-005, and anoptional panhandle 27-006 which facilitates mounting. Panhandle 27-006has a panhandle bottom face 27-007 and panhandle corner 27-008. On thefront face 27-002 is a viewing aperture 27-012. On the rear face 27-005is an image source aperture 27-014 adapted to cooperate with an imagesource 27-030, such as a CRT or television monitor. Disposed within thehousing 27-001 is a reflective element 27-035, such as a partiallyreflective mirror, that acts as a beamcombiner.

Part of the image source 27-030 is used as a foreground image source27-040. A foreground image 27-050 is on the foreground image source27-040. Another part of the image source 27-030 is used as a backgroundimage source 27-080. A virtual background image 27-090 appears displacedbehind the foreground image 27-050. Light path 27-100 shows the pathfrom the background image source 27-080 to the virtual background image27-090. A conventional mirror 27-135 is disposed within the housing27-001 to reflect light from the background image source 27-080 to thereflective element 27-035 which reflects light to a viewer 27-200.

As in other embodiments, reflective element 27-035 acts as abeamcombiner to present the co-aligned foreground image 27-050 and thebackground image 27-090 to a viewer 27-200. In this embodiment, however,the foreground image source 27-040 and the background image source27-080 are just different parts of the same image source 27-030. Thisembodiment is potentially smaller, cheaper, and easier to use thanembodiments which use more than one image source as the sources of theforeground image and the background image.

Optionally, the housing 27-001 may contain all sources of imagery,whether a single image source or multiple image sources. In thisembodiment, however, the housing 27-001 is optionally attached,permanently or temporarily, to the image source 27-030. For example,straps of fastening tape (such as Velcro) placed on the panhandle bottom27-007 are optionally used to attach the housing 27-001 to the imagesource 27-030. Velcro straps, hinges, a brace or other known fasteningdevices or schemes are optionally used to dispose the housing 27-001near the image source 27-030. The housing 27-001 is preferablycollapsible.

Embodiments of the present invention may vary widely in size, as notedelsewhere in this document. For example, the embodiment of FIG. 27 areoptionally made to fit a hand-held gaming device or a large projectiontelevision.

Referring now to FIG. 27A, the use of hinges at panhandle corner 27-008or Velcro straps on optional panhandle 27-006 can allow the housing27-001 to be flipped up onto the monitor.

FIG. 28 shows another single-image-source embodiment of the presentinvention. In FIG. 28, the embodiment has a housing 28-001. Housing28-001 has a front face which has a viewing aperture 28-012. The housing28-001 has on its rear face 28-005 an image source aperture 28-014.

Disposed near the image source aperture 28-014 is an image source28-030, such as a CRT or television monitor. Disposed within the housing28-001 is a reflective element 28-035, such as a partially reflectivemirror. Part of the image source 28-030 is used as a foreground imagesource 28-040. A foreground image 28-050 is on the foreground imagesource 28-040. Another part of the image source 28-030 is used as abackground image source 28-080. A virtual background image 28-090appears displaced behind the foreground image 28-050. Light path 28-100is shown. Light path 28-101 is shown. A conventional mirror 28-135 isdisposed within the housing 28-001 to reflect light from the backgroundimage source 28-080 to the reflective element 28-035 which reflectslight to a viewer 28-200.

As in some other embodiments, reflective element 28-035 acts as abeamcombiner to present the co-aligned foreground image 28-050 and thebackground image 28-090 to a viewer 28-200.

Light path 28-100 shows a proper line-of-sight from a viewer 2-200 tothe foreground image source 28-040 (and thus to the foreground image28-050, which is on its surface). Light path 28-101 shows a potentialproblem with this embodiment. A viewer 28-200 has line of the sight tothe background image source 28-080 through viewing aperture 28-012. Itis preferable that the user not have line-of-sight to the backgroundimage source 28-080 because it is distracting to the perception of 3-D aviewer 28-200 should perceive when looking at the co-aligned backgroundimage 28-090 and foreground image 28-050.

One way to avoid this problem is to make the viewing aperture 28-012smaller, to reduce the viewpoints from which a viewer 28-200 has aline-of-sight to the background image source 28-090.

Another way to avoid the problem of line-of-sight to the backgroundimage area is shown in FIG. 29. The embodiment shown in FIG. 29 has ahousing 29-001. Housing 29-001 has a top face 29-004 which has a viewingaperture 29-012. The housing 29-001 has on its rear face 29-005 an imagesource aperture 29-014.

Disposed near the image aperture 29-014 is an image source 29-030, suchas a CRT or television monitor. Disposed within the housing 29-001 is areflective element 29-035, such as a partially reflective mirror. Partof the image source 29-030 is used as a foreground image source 29-040.A virtual foreground image 29-050 is created by reflective element29-035. Another part of the image source 29-030 is used as a backgroundimage source 29-080. A virtual background image 29-090 appears displacedbehind the virtual foreground image 29-050. A conventional mirror 29-135is disposed within the housing 29-001 to reflect light from thebackground image source 29-080 to the reflective element 29-035 whichtransmits light to a viewer 29-200.

As in some other embodiments, reflective element 29-035 acts as abeamcombiner to present the co-aligned virtual foreground image 29-050and the virtual background image 29-090 to a viewer 29-200.

Light path 29-100 and light path 29-101 show a proper line-of-sight froma viewer 2-200 to the virtual foreground image source 29-050 and thevirtual background image source 29-090.

There is a potential problem with this embodiment, as the images aredirected at a ninety degree angle to the face of the image source. For aviewer 29-200 seated in a chair, for example, the image source 29-030 isplaced “face up” so the viewing aperture 29-012 is oriented to theviewer 29-200. In the alternative, the monitor is turned ninety degreesto its left, and the adapter directs its output to its right. Changingthe orientation of the image source, as with a television set orcomputer monitor, can be inconvenient and therefore undesirable (e.g.from a thermal management standpoint).

FIG. 30 shows the embodiment shown in FIG. 29, in which a secondaryreflective optic 29-400, such as a plane mirror, is used to direct theimages to a viewer 29-200 seated in front of a conventionally orientedmonitor or CRT.

Splitting a single image source, such as a television monitor orcomputer CRT, can create problems with the aspect ratio of the image.For example, splitting a television screen horizontally yields a verywide “landscape” or “letterbox” aspect ratio, while splitting itvertically yields a “portrait” aspect ratio. If the image that appearson the image source has been suitably compressed 2:1, additional optics,such as a cylindrical lens, are optionally used to expand the originalimage, if desired, to regain the desired aspect ratio.

Referring once again to FIG. 30, secondary reflective optic 29-400 isoptionally a cylindrical expansion mirror. The cylindrical expansionmirror is designed to uncompress the image in one direction. Thus theco-aligned foreground image 29-050 and background image 2-090 areredirected and expanded for a viewer 29-200. Anamorphic curvature of themirror can provide virtually any size image with any desired aspectratio.

Real Imaging

In FIG. 31 there is shown an image source 31-030, a real image 31-050, aviewer 31-200, and a Fresnel lens 31-300. In FIG. 32 there is an imagesource 31-030, a real image 31-050, an arrow 31-100, a viewer 31-200,and a Fresnel lens 31-300.

Any lens (whether Fresnel or conventional), if properly placed inrelation to an image source, can create a real image for a controlledangle of view. Image source 31-030 is re-imaged by Fresnel lens 31-300.This real image 31-300 is visible to a viewer 31-200 who is within acontrolled angle of view indicated by arrow 31-100. The size of the realimage

and the controlled angle of view can be altered by moving the imagesource, varying the focal length of the lens and relative position, etc.

A real image is an image in front of the optical element that reimagesit, unlike a virtual image which appears to be behind the optic. Forexample, an image in a mirror appears behind the glass. A real imagereimaged by a lens appears to float in space in front of the lens.

Fresnel lenses are preferred for most embodiments of the presentinvention that produce real images because they are relatively light andeasy to manufacture. Unlike many lens types, they are optionally gluedtogether in a sandwich, to correct for spherical aberration or chromaticaberration. For example, two or more different materials can be used inthe elements of the sandwich (or any of the other optical elementsdisclosed herein) to correct for chromatic aberration. Those of ordinaryskill in the art recognize that as other lenses become more economical,then other lenses may become preferred.

A properly placed Fresnel lens can re-image almost any image source.FIG. 32 is a single-image-source adapter of the present invention, suchas depicted in FIGS. 27 and 29.

FIGS. 32A and 32B depict a Fresnel lens 32A-300, which has additionalfacets 32A-301. FIG. 32A is a perspective view, and FIG. 32B is a planview. Facets 32A-301 help extend the controlled angle of view created bya Fresnel lens 32A-300 to nearly one hundred eighty degrees.Alternatively, the sheet forming the Fresnel lens 32A-300 is curved intoa cylinder.

Referring now to FIG. 33, housing 33-001 has a front face 33-002, a topface 33-004, and a rear face 33-005. The housing 33-001 has on its frontface 33-002 a viewing aperture 33-012. The housing 33-001 has on itsrear face 33-005 an image source aperture 33-014.

Disposed near the image source aperture 33-014 is an image source33-030, such as a CRT or television monitor. Disposed within the housing33-001 is a reflective element 33-035, such as a partially reflectivemirror. Part of the image source 33-030 is used as a foreground imagesource 33-040. A real foreground image 33-050 is formed. Another part ofthe image source 33-030 is used as a background image source 33-080. Areal background image 33-090 appears displaced behind the realforeground image 33-050. A conventional mirror 33-135 is disposed withinthe housing 33-001 to reflect light from the background image source33-080 to the reflective element 33-035 which reflects light to a viewer33-200. Fresnel lens 33-300 is disposed between the reflective element33-035 and the viewer 33-200.

As in other embodiments, reflective element 33-035 acts as abeamcombiner to present the co-aligned foreground image 33-050 and thebackground image 33-090 to a viewer 33-200. The light from thebackground image source 33-080 is reimaged into real background image33-090. The light from the foreground image source 33-040 is reimagedinto the real foreground image 33-050.

The viewer 33-200 sees the real foreground image 33-050 and the realbackground image 33-090 hanging in space in front of all opticalelements. The viewer 33-200 is often startled, expecting to find a planeof glass from which the real foreground image 33-050 and the realbackground image 33-090 are reflected. In this embodiment, the viewer33-200 can place her finger on or through the foreground image 33-050 ifdesired, and still see the rest of the scene.

Other embodiments of the present invention may also utilize a lens,preferably a Fresnel lens, to generate at least one real image.

FIG. 34 is another embodiment of the present invention which utilizes aFresnel lens to generate a real image. Depicted in FIG. 34 arereflective means (such as a beamsplitter) 34-035, foreground imagesource 34-040, real foreground image 34-051, real foreground image34-052, background image source 34-080, a first viewer 34-202, a secondviewer 34-202, and a Fresnel lens 34-300.

This embodiment uses a real foreground image 34-051 and/or 34-052. Aviewer 34-201 sees the real foreground image 34-051 and has a directline of sight to the background image source 34-080. A viewer 34-202sees the real foreground image 34-052 and sees the virtual image of thebackground image source 34-052. Real image 34-051 is reflected byreflective means 34-035, and real image 34-052 is transmitted byreflective means 34-035.

A housing is optionally used which allows viewing from the position ofviewer 24-201, viewer 24-202 or preferably both. An embodiment whichallows viewing in such positions turns FIG. 2's “misdirected” light1-102 and 1-103 into a potentially desirable feature of the invention.

As in other embodiments, reflective element 34-035 acts as abeamcombiner to present the co-aligned real foreground image and thebackground image to a viewer. The light from the foreground image source34-040 is reimaged into the real foreground image 34-050.

The main difference between the embodiments of FIG. 33 and of FIG. 34 isthe placement of the Fresnel lens 33-300. In FIG. 33, the Fresnel lens33-300 is disposed between the foreground image source 33-040 and thereflective element 33-035. In the embodiment in FIG. 34, only theforeground image is a real image. The background image is a virtualimage or a direct line of sight to the background image. By placing aFresnel lens in an appropriate place in the light path, any or all imageplanes are reimaged into a real image.

FIG. 41 shows a single image source 3-D adapter as in FIG. 28. With theaddition of the Fresnel lens, a viewer sees a real foreground image anda real background image. The optics are optionally placed that the realimages appear to float in space in front of the housing and allaccompanying optics.

When first presented with a real image, the viewer often expects it tobe a projection on some type of screen. For many embodiments, the viewercan actually place his or her hand in plane with the image, much totheir surprise. The use of real images can greatly contribute to theperception of depth in the scene.

The Fresnel lens may alternately be placed so as to “float” only theforeground image or only the background image. Multiple Fresnel lensesare optionally placed to refocus light in a shorter optical path, forexample.

A more compact embodiment of the present invention uses a singleprojector (of any standard type as known in the art) as the source offoreground and background images.

One portion of the image projected by the beam from the projector lensis the foreground, while another portion is the background.

Consider what one sees on a screen that is perpendicular to theprojection beam and is moved progressively farther away from theprojection lens until the image comes into focus. At first for a certainshort distance, the image is so out-of-focus that the beam appears as ifit is homogeneous. Beyond that distance, the image is more nearly infocus and is susceptible of being split. This is subject to empiricaldetermination.

That is, if one positions the screen so that the image is in focus andthen slowly inserts an opaque object such as a sheet of cardboard intothe path of the beam between the projector and the screen within thatcertain short distance, the entire image becomes progressively dimmer.Farther out from the projector than that certain short distance, whenone similarly inserts such an object between the projector and screen,the image becomes partially eclipsed.

This more compact embodiment of the present invention uses a mirror thatis placed far enough out from the projector exit lens to divert portionsof the projector's output to different projection screens. It isimportant that the mirror be placed far enough out from the projectorthan that certain short distance, so the image is actually split ratherthan dimmed. For a typical projector the inventor has found that themirror should be at least twelve inches and preferably about 18 inchesfrom the projector exit lens face.

A portion of the beam is reflected to a projection screen. Anotherportion of the beam is reflected to a second projection screen, disposedat a ninety-degree angle from the first projection screen. Preferably, alens is used to re-focus one of the portions, since the screens are atdifferent distances from the projector. Each portion reflects from itsscreen to a beamcombiner whereby the portions are aligned. One portionis transmitted while the other portion is reflected in the samedirection.

Once the foreground and background images are so aligned, they areredirected, refocused into real images, magnified, corrected for aspectratio, for distortion, etc., as elsewhere taught in this document.

Referring in particular to FIG. 34A, light ray 34A-101 leaves projector34A-030 and reflects from a reflective element 34A-135 (preferably aplane mirror). By the time light ray 34A-101 by-passes reflectiveelement 34A-136 (preferably a plane mirror) it contains only light whichwill eventually comprise the foreground image 34A-050. Light ray 34A-101hits projection screen 34A-040, reflects back to a reflective element34A-035, which acts as a beamcombiner, from which light ray 34A-101reflects to a secondary reflective optic 34A-400, preferably a planemirror, from which it is reimaged by a first Fresnel (or lenserF) lens34A-301 and a second Fresnel (or lenserF) lens 34A-302. As aconsequence, a real foreground image 34A-050 appears in space welloutside the housing 34A-001.

Light ray 34A-102 is reflected by reflective element 34A-136, preferablya mirror, at a point when light ray 34A-102 is far enough from theprojector that it contains only light that will comprise the backgroundimage. Light ray 34A-102 then hits the background projection screen34A-080, from which it reflects through the reflective element 34A-035.Co-aligned with the light ray 34A-101 reflected from 34A-035, light ray34A-102 is reflected and reimaged as a real background image 34A-090outside the housing 34A-101. Varying the distances and arrangements ofthis embodiment in light of the rest of this document is a part of theinvention.

One of light ray 34A-101 or 34A-102 is focussed by a lens 34A-031 sinceforeground projection screen 34A-040 and background projection screen34A-080 are at different distances from the projector 34A-030. If lightray 34A-102 is focussed, a negative lens is used. Preferably light ray34A-102 is focussed instead, so more plentiful positive lenses may beused.

FIG. 34B is a plan view of an image display system of the presentinvention. Foreground projector 34B-030 projects onto curved projectionscreen 34B-040. Mirror 34B-135 and mirror 34B-136 reflect and reimagelight from the curved projection screen 34B-040 into a real foregroundimage 34B-050. Viewer 34B-200 sees a virtual background image 34B-090,the reflection of background projection screen 34B-080 from reflectiveelement 34B-035.

Mirror 34B-135 and 34B-136 are curved Fresnel mirrors, faceted Fresnelmirrors (as shown in FIGS. 32A and 32B), planar Fresnel mirrors orequivalent optics. As noted elsewhere in the application, either or bothimage source may be curved. Preferably the background image is curved totake create a “Cinerama” effect described in the Background of theInvention.

FIG. 34C is a plan view of an image display system of the presentinvention similar to the one shown in FIG. 34B. In this embodiment,mirror 34C-300 is an off-axis Fresnel mirror and mirror 34C-301 is aFresnel mirror.

Some embodiments of the display adapter use one or more lenses topresent one or more real images to the viewer. While virtual images are“behind the glass,” real images appear to leap from the optics and arean “above the glass” experience.

An image source placed at approximately 2F (twice the focal length) onone side of a lens causes a real image to form in space at approximately2F on the other side of the lens. The exact location of the lens can beselected to increase or decrease the size of the final “floating” image.In many of the embodiments, at least one lens is placed so as to floatat least the foreground image, the background image or both.

Fresnel Lens

In accordance with the present invention, an improved Fresnel lens ispreferably employed. In general, a Fresnel lens is an optical elementresembling a plano-convex or plano-concave lens that is cut into narrowrings and flattened out. Fresnel lenses can be large glass structures asin lighthouses, floodlights or traffic signals, or thin molded plasticplates with fine steps.

Fresnel lenses are commonly made from plastic, thus allowing them to bemass-produced inexpensively and quickly from a metal master. The metalmaster is typically made by rotating a copper or other material blankwith a computer-manipulated cutting tool of diamond or other hardmaterial. The master is then used to cast, emboss, compression mold orinjection mold plastic replicas.

Conventional Fresnel lenses are formed with a series of annular ringsand are therefore relatively thin, and relatively light. In contrast,conventional plano-convex and plano-concave lenses are thick, heavy, andexpensive.

Fresnel lenses have poor resolving power when compared to conventionallenses because of the shape of the surface of each annulus. Each annulusof a Fresnel lens, when viewed in cross-section, has a vertical surface(a rise) and a lens-function surface (a face). Together the facestherefore merely approximate the desired curvature of the lens.

Annular lenses, such as Fresnel lenses, also suffer from flare orscatter of light as some of the light passes through and reflects off ofthe rise instead of through the lens face. To improve the opticalperformance of annular lenses, the amount of such light scattered by therises should be reduced to a minimum.

Earlier workers have disclosed scratching or abrading the rises ofFresnel lenses. However, such methods do not provide a satisfactorysolution to the problem of scattered light because the amount ofscattered light is not reduced; rather it is merely scattered and flaredin a different way.

The “lenserF” is another type of annular lens. The lenserF provides alens which has as one side a series of spaced ring-shaped planar, orannular, faces, which together approximate the planar surface of anormal plano-convex or plano-concave lens. The annular faces areseparated by rises. The concentric annular faces are reminiscent of aFresnel lens, but with the planar face being stepped, rather than thecurved face as in a Fresnel lens. Thus the name: “lenserF” is “Fresnel”spelled backwards.

A lenserF is thin, but, unlike a Fresnel, it is not flat. It retains thecurved shape and depth of the plano-convex or plano-concave lens, andprovides much better resolving power than a corresponding Fresnel lensthat approximates the same curve. The effect of such a curvature is tocreate a cavity in which additional lenses (lenserFs or others) can beplaced. Compounding or cascading of lenses can take place in a muchsmaller volume, allowing lenses to be closer together than withconventional lenses (allowing greater magnification, chromaticaberration correction, lower F number, etc.). Compound plastic lensesare capable of being made to minimize chromatic aberration.

An improvement to annular lenses, including Fresnel and lenserF lenses,disclosed herein comprises means for decreasing the amount of lightscattered from the rises of the lens.

A number of techniques are disclosed herein which are optionally usedalone, or in combination with scratching or abrading the rises, toreduce the light reflecting from the rises. These include: (1) coatingthe rise with opaque material; (2) applying an anti-reflective (AR)coating to the annuli of the lens; (3) pressing the lens from a blankhaving pre-printed opaque rings so that the pre-printed rings cover therises of the lens; (4) using a transparent wave-retardation sheet inconjunction with polarized light; (5) using an opaque annular ring maskin conjunction with the lens; and (6) using photographic exposures ofrings onto photosensitized rises and employing hydrophilic andhydrophobic coatings, copper over-coated with nickel with acid etchedrings in the nickel, greasy ink, and water.

Specific substances appropriate to these purposes are known to those ofskill in chemical technology. This information may be ascertained fromcustomary reference works in this field, including for example theKirk-Othmer Encyclopedia of Chemical Technology, Beilstein's Handbuch,and Chemical Abstracts.

These methods will be described below in greater detail using as anexample an annular lens. However, it is to be understood that they aresimilarly applicable to other optical elements having rises.

One method employs coating the rises of the lens with an opaqueabsorptive material. Generally, an opaque material such as ink is madeto adhere to the rise, while leaving other portions of the lens free ofopaque material. The rise portion of the lens is preferably scratched,abraded or scored during manufacture to promote better adherence ofopaque material to the rise portion.

(1a) The rise is desirably scratched, abraded or scored duringmanufacture to facilitate adherence. Opaque material such as ink maythereafter be applied to an annular lens or other optical element bydipping, spraying or other conventional means, then subjecting it to abrief wash, with or without wiping by rubber or other material withappropriate grooves. Such a technique results in a coat of ink adheringto the scratched rise and leaves the smooth lens faces uncoated.

(1b) In another embodiment of the invention, the application of opaquematerial to selected areas of an annular lens is optionally achieved bythe use of a photoresist. The photoresist is then used to protect thecoated regions of the lens from the opaque material. This embodiment ofthe invention is optionally implemented by applying a coating ofpositive photoresist to the entire lens. Positive photoresist generallysoftens or depolymerizes upon exposure to light. A light shield with anappropriate opening (e.g. wedge-shaped) is then placed over the lens, sothat when the lens is exposed to light from the proper angle, the facesare not exposed to light. The lens is rotated to provide successiveexposure of the lens rises around the entire 360 degrees. By thisprocess the rises, but not the faces, are exposed to light. A resistdeveloper is then used to rinse away the photoresist from the rises,while leaving the unexposed photoresist on the face portions. The entirelens can then be coated with opaque material that is capable of adheringto the lens rises but that is prevented from adhering to the lens facesbecause of the presence of the photoresist thereon. The photoresist isthen removed from the lens faces by further rinsing with developer todissolve away the unexposed resist together with the opaque materialcoating it. This process leaves rises coated with opaque material andclear faces.

(1c) Yet another embodiment of the invention that uses a negativephotoresist is as follows. Negative photoresist generally hardens orpolymerizes upon exposure to light. As in the method described insection (1b) above, the lens is dipped or sprayed in photoresist andthen exposed to a properly masked light. In this method, however thelight exposure is arranged to strike the resist only on the faces. Adeveloper will rinse away the unexposed negative photoresist from therises. Coating of the lens with opaque material, and removal ofremaining resist and opaque material from the races is then performed asdisclosed above.

(1d) Yet another embodiment of the invention involves using aphotoresist that is black or other dark color, dyed black or other darkcolor, or is otherwise opaque once the process is finished. With properexposure and development, e.g. as described above, the rises are leftcoated with the black resist, while the faces are left uncoated.

(1e) In another embodiment of the invention, pre-printed opaque rings orstriations are positioned on material such as flat plastic such thatwhen the lens or other optical element is pressed, stamped, embossed ormolded, the rise portions of the completed lens will be made up of theopaque pre-printed rings.

(1f) In yet another embodiment, a transparent element having pre-printedthereon opaque lines or circles is positioned with respect to the risesof an existing stepped optical element such that the opaque markingsintercept a substantial portion of the light which passes through, orwhich reflects off of, the rises. Optionally the opaque markings may beon the reverse side of the substrate from which the optical element isconstructed.

(1g) In another embodiment, emulsion coated on both faces and rises ofthe lens are scanned by laser or exposed to an annular pattern to becomedark on rises while being clear on faces after standard photographicdevelopment.

(1h) In another embodiment, grooves are formed in the lens surface whenthe lens is made. Then ink is put on and “doctor bladed” off, leavingink in the grooves. Drying of the ink can be done by air, UV, heat, etc.

(2) Another embodiment of the invention involves applying anantireflective coating to virtually all surfaces of the lens to reducereflection of any light from it. This embodiment of the inventioneffects its result in a manner similar to the way in which an AR coatingon a television tube eliminates the reflections from room lights. Inthis embodiment of the invention, an AR coating applied to the Fresnellens also coats the rises, thus reducing the reflection of light thatimpinges on or reflects from the rises.

Yet a further embodiment of the invention includes an AR coating onvirtually all surfaces of an annular lens and an opaque coating on therises. This embodiment combines a reduction of light reflected from thefaces and an absorption of light that would otherwise pass outwardlythrough the rises, to further reduce light passing through or reflectingfrom the rise portions.

(3) In another embodiment of the invention, scattering from the rises ofthe lens is reduced by using an image source that produces circularlypolarized light. Such an image source is optionally an LCD inconjunction with an appropriate polarizer, or it is optionally anothersource of light that has been circularly polarized. In this embodiment,only light which passes through the lens face directly without beingreflected from the rise will be transmitted by a circular analyzer.

Annular Lens Embodiments

FIG. 35A shows a plan view of a Fresnel lens 35-300 of the prior art.FIG. 35B is a cross-sectional view of a Fresnel lens 35-300, taken atline 35B-35B. Shown is a rise portion 35-310 and a face portion 35-315.

LenserF lenses are shown in FIGS. 36 and 37. FIG. 36 shows a crosssection of a plano-concave lenserF 36-300, which has rise portion 36-310and a face portion 36-315. FIG. 37 shows a cross section of aplano-convex lenserF 37-300.

In FIG. 38 are shown details of a Fresnel lens 38-300 in cross-sectionalview. Light ray 38-100 is shown. Rise portion 38-310 and face portion38-315 are depicted.

Light ray 38-100 passes through rise portion 38-310. Light ray 38-100then reflects from face portion 38-315, contributing to scatter orflare.

FIG. 39 shows details of a Fresnel lens 39-300 in cross-sectional view.Light rays 39-101, 39-102, and 39-103 are shown. Also shown is scoredrise 39-310. FIG. 39 schematically illustrates additional scatter orflare arising from light ray 39-101 being reflected from a scratchedrise 39-310 of a prior art Fresnel lens. Light ray 39-102 is shown toproduce additional scatter or flare as it passes through the scored rise39-310 and is refracted. Light ray 39-102 is shown to contributeadditional scatter and flare. Light ray 39-103 contributes to scatterand flare.

FIG. 40 shows light rays 40-100, 40-101, 40-102, and 40-103. FIG. 40also shows details of a Fresnel lens 40-300 in cross-sectional view.Also shown are each opaque rise portion 40-320. Light rays 40-100,40-101, 40-102, and 40-103 are each shown to be absorbed upon hittingthe rise portion 40-320.

In accordance with the present invention, an opaque material such as inkor other coating material is made to adhere to the rise, while leavingother portions of the lens free of opaque material. The rise of the lensis preferably scratched, abraded or scored during manufacture to promotebetter adherence of material to the rise.

Opaque material is optionally applied to a lens by dipping or sprayingthe lens with a coating such as ink, then subjecting the lens to a briefwash. Such a technique results in a coat of ink adhering to thescratched rise and leaves each smooth lens face uncoated.

FIG. 41 shows another way to provide such opacity using photoresist on aFresnel lens 41-300. A light shield 41-328 with a wedge-shaped opening41-329 is shown. FIG. 42 is a cross sectional view of FIG. 41 takenalong line 42. Light rays 41-100 and 41-101 are shown. Unexposedphotoresist 41-322 is shown. Exposed photoresist 41-324 is shown. Alsoshown is light shield 41-328.

In an embodiment of the lens improvement, the application of opaquematerial to each rise of the lens is optionally achieved by the use of aphotoresist. This embodiment of the invention is optionally implementedby applying a coating of negative photoresist to the entire lens 41-300.A light shield 41-328 with a wedge-shaped opening 41-329 is then placedover the lens 41-300, so that when the lens is exposed to light as fromlight ray 41-100 from the proper angle, each rise 41-310 is not exposedto light. The lens 41-300 is rotated to provide successive exposure ofeach lens face 41-315 around the entire 360 degrees. By this processeach face 41-315, but not any rise 41-310, is exposed to light.

A resist developer is then used to rinse away the photoresist from eachrise 41-310, while leaving the exposed photoresist on each face 41-315.The entire lens 41-300 can then be coated with opaque material that iscapable of adhering to the lens 41-300 but that is prevented fromadhering to the lens faces because of the presence of the photoresistthereon. The photoresist is then removed from each face 44-315 byfurther rinsing with developer to dissolve away the exposed resist41-324 together with the opaque material coating it. This process leaveseach rise 41-310 coated with opaque material and every face 41-315clear.

Yet another embodiment of the invention that uses a positive photoresistis as follows. As in the method described above, the lens 41-300 isdipped or sprayed in photoresist and then exposed to a properly maskedlight. In this method, however, the light exposure is arranged to strikethe resist only on each rise 41-310. A developer will rinse away theexposed positive photoresist from each rise 41-310. Coating of the lens41-300 with opaque material is performed as disclosed above. The resistis developed away each face 41-315.

Yet another embodiment of the invention involves using a photoresistthat is dyed dark. With proper exposure and development, each rise41-310 is left coated with the black resist, while each face 41-315 isleft uncoated.

Referring now to FIG. 43, in another embodiment of the invention thereare opaque pre-printed rings 43-340 positioned on lens material 43-342.The opaque pre-printed rings 43-340 are positioned such that when a lens44-300 is pressed, stamped, embossed or molded, each rise 44-310 of thecompleted lens 44-300 will be made up of the opaque pre-printed rings44-390.

FIG. 45 shows an embodiment involving circularly polarized light. Lightray 45-100, light ray 45-101, and light ray reference point 45-102 areshown. Also shown are the Fresnel lens 45-300, each rise portion 45-310,each face portion 45-315, and a circular polarizer 45-350.

Scattering from each rise 45-310 of the lens 45-300 is reduced byproviding an image source that produces circularly polarized light. Suchlight is optionally provided by the output from an LCD or is optionallyother light that has been circularly polarized. In this embodiment, acircular polarizer 45-350 is provided so that light ray 45-100 whichpasses through the face will be properly transmitted by circularpolarizer 45-350. However, when light ray 45-101 reflects from the rise45-310 at light reference point 45-102, its polarization will change andit will not pass through the circular polarizer plate 45-350.

Referring now to FIG. 46, another embodiment of the invention involvesapplying an anti-reflective (AR) coating to the lens 46-300 to reducereflection of any light from any face 46-315 and any rise 46-310. Thisembodiment of the invention effects its result in a manner similar tothe way in which an AR coating on a television tube eliminates thereflections from room lights. In this embodiment of the invention an ARcoating 46-355 applied to the Fresnel lens also coats each rise 46-310,thus reducing the reflection of light 46-100 that passes through thelens 46-300.

Yet a further embodiment of the invention uses an AR coating togetherwith an opaque coating 46-355. This embodiment combines a reduction oflight reflected from any face 46-315 and an absorption of light tofurther reduce light passing through or reflecting from any rise 46-310.

Another embodiment of the single-image-source 3-D display adapterinvention uses a special “sandwich” of optical elements, some of whichhave been invented for this purpose. It has the advantage of lightweight when the elements are annular or Fresnel-type elements aretypically formed from plastic sheets and are relatively simple andinexpensive to fabricate.

The three sandwich elements in combination create a pair of co-axialdisplaced images: a foreground image on the image source, and a virtualbackground image which appears behind the foreground image. The Fresnelcylinder lens is optionally used to regain image size and restore aspectratio.

The following description provides details for an illustrativeembodiment for use with a standard 17-inch screen, but of course thisinvention is readily adapted for use on monitors or television sets ofother sizes using calculations known to those in the art. On atelevision screen or computer monitor measuring thirteen inches in thehorizontal and ten inches in the vertical dimension, the top portion ofthe screen is the foreground image source, and the bottom portion of thescreen is the background image source. The lens element “sandwich” ofthe present invention is placed parallel to the screen. In theembodiment being described, it is spaced about eight inches (8″) fromthe front of the screen. The lens element sandwich is optionally placedin a collapsible housing, attached to the monitor with L-brackets,mounted to a base, or secured by other means known in the art.

The lens element sandwich comprises a Fresnel semi-lens and a Fresnelbeamcombining element. Optionally it also includes a Fresnel cylinderlens if it is desired to modify the aspect ratio of the displayed image,e.g. where it is desired to double the height of the images displayed onthe image source.

The first element of the lens element sandwich is a novel opticalelement that is hereby disclosed, which the inventor calls a Fresnelsemi-lens 46A-700. It is designed to permit the viewer to view aforeground image at the position of the image source (the face of thetelevision tube) and a virtual background image which appears fourinches behind the foreground image. It consists of alternating sets ofsegments, one set 46A-701 of segments being part of a Fresnel lens andthe other set 46A-702 of segments being parallel to the baseline of thesheet (flat). The segments are preferably in the form of narrowhorizontal stripes but may take other shapes if desired. In theembodiment being specifically described as an example, the segments thatare part of a Fresnel lens have a focal length of twenty-four inches.Light which passes through the Fresnel semi-lens faces will thus bereimaged as a virtual image four inches behind the image source,magnified 1.5 times.

The Fresnel semi-lens is a generally sheetlike optical element that isgrooved on one side, having circular grooves that form rises and faces.In a conventional Fresnel lens, the faces approximate the curvature of aregular optical lens. In the Fresnel semi-lens of the present invention,only a portion of the area of the optical element approximates thecurvature of a convex (or for other purposes, a concave) optical lens)while the rest of the area of the Fresnel semi-lens is parallel to thebaseline (i.e. flat) and thus permits light along the axis to passthrough unrefracted. The Fresnel semi-lens is constructed to cooperatewith the Fresnel beam combining element to produce the desired overalleffect.

The Fresnel beamcombining element can be in one of two forms: a Fresnelbeamcombiner 46B-800 or a Fresnel semi-prism 46D-800. The function ofthis element is to bring the foreground image and the background imageinto alignment, as discussed hereinabove in connection with otherembodiments of the overall invention. Either form of the Fresnelbeamcombining element is sufficiently fine (as measured, for example, ingrooves on the order of a millimeter or less) to be unresolvable by thehuman eye. This characteristic is also desirable for the Fresnelsemi-lens.

The specifics of how and where the Fresnel beamcombining element bringsthe image into alignment are somewhat different from those of thepreviously described embodiments utilizing reflective optics and meritfurther discussion.

By Fresnel beamcombiner 46B-800, the inventor means a generallysheetlike optical element, preferably of plastic such as acrylic, thatis grooved on one side. Unlike a Fresnel lens, where the grooves arecircular and form rises and faces, a Fresnel beamcombiner 46B-800 has aregular series of linear grooves that are isosceles triangular in crosssection. The faces of each such triangle on the left side form a firstset of facets that tend to act in unison on light from a particularsource, and the faces of each such triangle on the right side form asecond set of facets that similarly tend to act in unison. Commercialproducts that can be so employed are available from Fresnel Optics,Inc., Henrietta, N.Y., in the PR 700 series of catalog numbers(identified as beamsplitters, since a beam going in the oppositedirection from the combined beam produced by the present invention issplit into two directions).

In embodiments wherein the Fresnel beam combining element is a Fresnelbeamcombiner, a viewer sees light from the light source through each ofthe two sets of facets. Light from the top half of the monitor comingthrough one set 46B-801 of facets of the Fresnel beamcombiner is benttoward the viewer. Similarly, light from the bottom half of the monitorcoming through the other set 46B-802 of facets of the Fresnelbeamcombiner 46B-800 is correspondingly bent in the opposite directionand also directed towards the viewer. The angle between the input beamsin this embodiment is approximately thirty-five degrees. Light from thetop half of the image source and light from its bottom half are thusco-aligned: from the viewer's vantage point the foreground image fromthe top half of the monitor is superimposed on the background image,from the bottom half of the monitor, in line with the center of theimage source.

As an alternative embodiment, the Fresnel beam combining element is anovel optical element that is hereby disclosed, which the inventor callsa Fresnel semi-prism. To describe the novel Fresnel semi-prism, theinventor needs first to discuss conventional Fresnel prisms.Conventional Fresnel prisms are available from Fresnel Optics, Inc. inthe PR 600 and PR 700 series of catalog numbers. A Fresnel prism is alsoa generally sheetlike optical element that is grooved on one side. Itsfaces consist of straight lines that are all sloped the same angle tothe baseline of the sheet. Its rises approximate the vertical, as in aFresnel lens, but they are linear rather than circular. A Fresnel prismdiffers from a Fresnel beamcombiner in that its cross section showsrepeating right triangles, rather than isosceles triangles.

Just as a convex Fresnel lens tends to focus light from a source much asthe corresponding planoconvex (regular) lens does, a Fresnel prismrefracts light from a source much as a regular right-triangular prismdoes. If one looks at a scene and then at the same scene through aFresnel prism, the scene appears to be offset from its actual position.When the lines of the Fresnel prism are oriented horizontally, theapparent offset is vertical.

A Fresnel semi-prism is a kind of Fresnel beam combining element thatpresents to the viewer, in one co-axial orientation, light beamsderiving from images in two different locations, e.g. on two differentareas of a television screen. It does this by refracting light beamsoriginating from one location and by passing directly without refractionlight beams originating from the other location.

Conceptually, to convert a conventional Fresnel prism into the Fresnelsemi-prism of the present invention, a certain portion of the diagonalfaces are, in effect, replaced with flat clear faces. In one form ofFresnel semi-prism each diagonal face alternates with a flat face.Similarly to the situation mentioned above with regard to the Fresnelsemi-lenses of the present invention, e.g. if the need is to control thebrightness ratio between one image source and the other, it isoptionally desirable to vary the proportion of the total area of flatfaces as compared to the total area of diagonal faces. Variousarrangements of faces are within the scope of the invention of a Fresnelsemi-prism, the important point being that it contains flat clear areasin some interdispersed distribution with prismatic areas. In use, lightfrom the bottom half of the image source (e.g. television tube face)passes through a prism portion of the Fresnel semi-prism and isrefracted so it is co-aligned with light from the top half of the imagesource. Light from the top half of the source passes through thenon-prism or flat portion of Fresnel semi-prism, and its direction isunchanged. Thus the foreground image and background image are co-axiallyaligned from the vantage point of the viewer.

As mentioned above, the Fresnel semi-lens acts on light coming from thebottom half of the display (such as a CRT) to create a virtual imagethat is behind the face of the display (i.e. the face of the CRT). Whenviewed coaxially with the image from the top half of the screen thatappears coplanar with the face of the tube, the viewer perceives areal-depth experience as described hereinabove.

A third, optional, element of the sandwich of optical elements of thepresent embodiment is a Fresnel cylinder lens, such as those fromFresnel Optics, Inc. in the catalog number series CY 500. In theembodiment being described, it desirably has a focal length of aboutsixteen inches. The images on the screen are each pre-compressed 2:1 inthe vertical. The Fresnel cylinder lens acts to expand the picture tocompensate for 2:1 vertical compression as discussed hereinabove,restoring aspect ratio and image size. This element is not necessary ifrestoration of aspect ratio is not desired. If it is not used, then theimages are not pre-compressed in the vertical dimension.

Since the Fresnel beam combining element needs to be carefully alignedwith the Fresnel semi-lens element, these two elements are preferablyembossed or molded on opposite sides of the same plastic substrate. Theflat faces on the Fresnel semi-prism and the flat areas of the Fresnelsemi-lens are aligned so that the light from the top half of the screenis not re-imaged for the viewer by the Fresnel lens segments. TheFresnel lens segments of the Fresnel semi-lens are aligned with theoptically refractive elements of the Fresnel beam combining element. Ifthe Fresnel beamcombiner is used as the Fresnel beam combining element,the bottom half of each prism sub-element is lined up with a clearsegment of the Fresnel semi-lens. Using either embodiment, light fromthe bottom half of the screen which passes through the Fresnel lenssegments of the Fresnel semi-lens is reimaged as a virtual image aboutfour inches behind the image source.

Alternatively a holographic optical element may be constructed (usingknown techniques) with the equivalent functionality of the two or threesubelements of the Fresnel sandwich described herein to accomplish thesame tasks.

Multiplayer 3-D Adapter

A further embodiment of the invention disclosed herein is a multiplayer3-D adapter. As in the single-image-source 3-D adapters, the output ofan image source (such as a television monitor or other standard CRT) issegmented. However, instead of being segmented into a single foregroundsection and a single background section, the screen is divided intomultiple foreground sections and multiple background sections. One setof foreground and background images is routed to each player (or viewer)preferably in a manner which does not allow any other player to seeanother player's view.

In one embodiment, for example, a computer screen is split vertically.The right-hand portion of the screen is the first player image source.The left-hand portion is the second player image source. The right-handportion is further subdivided into a foreground image section and abackground image section as discussed hereinabove. Also, as previouslydiscussed, the foreground image and the background image are co-alignedusing reflective elements such as a beamcombiner. Additional optics areoptionally used to re-direct and magnify the 3-D scene so that it is notvisible from the second player's seating position. The same is done forthe second player's image source.

Another embodiment splits the image source horizontally. The top of theimage source is used as a first player section, and the bottom of theimage source is used as a second player section. The upper left corneris used as the first player's background source, and the upper right isused as the first player's foreground source. A conventional mirror isused to reflect the background source to a reflective element which isused to co-align foreground and background images. Secondary optics,such as a conventional mirror, are optionally added to redirect theoutput to a seating position in front of the image source. Additionally,a Fresnel lens (or other reimaging optics) is optionally used to createa real image for a controlled angle of view. The controlled angle ofview can be made so that the second player may not see the firstplayer's image. The lower right corner is used as the second player'sbackground source. The lower left corner is used as the second player'sforeground source. Again, the images are co-aligned and preferablyredirected so that the first player can not see the second player'simage.

Dividing the screen into four player sections is optionally done aswell. Each quadrant is further subdivided into foreground and backgroundareas which are co-aligned. Again, they are preferably presented so thatother players do not have a view of the screen. The secondary optics arepreferably arranged so that all players sit in front of the monitor orso that the players may surround the monitor in various seatingconfigurations.

A multiplayer adapter (whether or not 3-D) allows inexpensive homesystems (like Sega Genesis, Nintendo or personal computers) to letpeople play multiplayer games that are preferably all of these:simultaneous, secret, multiperspective, multiplayer, non-networked. Inthe following paragraphs, current games will be examined that aremissing at least one from that group of attributes.

Simultaneous action is lost in serial play: where first one player takesa turn and then another player takes hers. Games like Stratego orBattleship do not have simultaneous action, although they use secretmultiperspectives in a non-networked game.

Some car racing games are multiperspective, and even split the monitorscreen to provide each driver with his own view. These games lack thesecret element because a player can simply look at the other player'sportion of the screen. In the car racing game, that is largelyunimportant, but in other games where stealth is a part of the actionfor example, secrecy is paramount.

Multiperspective is missing from a number of the “fight” games on themarket (Virtua Fighter, Mortal Kombat). The contestants are shownbattling it out in a ring from a shared perspective.

Multiplayer games like Doom, Heretic and Descent are currently playedover networks: more than one machine and some connective means isrequired to play the game. For example they use a port-to-portconnection, modem connection, local-area or wide-area network (LAN orWAN) connection, dial-up service (such as DWANGO) or the Internet. Atthe very least, a second image source is often used (i.e. a secondmonitor in some video arcade games).

Kali software (World Wide Web http://www.kali.com) allows people to playgames over the Internet as if players were on the same local areanetwork. TheLadder (World Wide Web http://www.theladder.com) hostsworld-wide ranking systems for thousands of individuals and teams whoplay Doom, Descent, and WarCraft II.

The addition of the connective means makes it much more expensive andinconvenient to play games where a secret, multiperspective isimportant. The multiplayer adapter of the present invention solves allof those problems: on it one can play games that are simultaneous,secret, multiperspective, multiplayer, and yet non-networked.

As an example, two players can play Doom using the present multiplayeradapter. Doom is a “first person” game, that is, the player's view iswhat his character sees as he runs around in a maze, killing things. Soif the first player sneaks up from behind the second player, the firstplayer will see the second player, who may remain unaware of the firstplayer's presence. As anyone who has played “twitch” games can attest:surprise is one of the fun parts.

In (non 3-D) multiplayer adapter, the output of a standard CRT is splitand each portion is directed to a different player by the use ofmirrors. This allows two players that share the same monitor to haveindependent and “secret” views of the computer screen. Additionaldivisions of the screen, as well as additional reflecting and/ormagnifying optics, allow the game action to be routed to many playersfrom the same monitor. The players may sit on different sides of themonitor or on the same side, depending on the embodiment.

FIG. 47 shows an image source 47-030. FIG. 47A shows a plan view of amultiplayer 3-D imaging system. FIG. 48 shows a perspective view of amultiplayer 3-D imaging system. Depicted are: First reflective element47-035 a second reflective element 47-036. First foreground image source47-040 and second foreground image source 47-041. First background imagesource 47-080 and second background image source 47-081. Firstconventional mirror 47-135 and second conventional mirror 47-136. Firstspherical mirror 47-400 and second spherical mirror 47-401.

Just as the single-image-source-adapter segments an image source into asingle foreground image source and a single background image source, themultiplayer adapter segments an image source into multiple foregroundimage sources and multiple background image sources. This embodimentsegments the image source 47-030 into a first foreground image source47-040 and a first background image source 47-080. First backgroundimage source 47-080 is reflected from a first conventional mirror 47-135to the first reflective element 47-035. Light from the foreground imagesource is reflected from the first reflective element 47-035. Thus, asin other embodiments, first reflective element 47-035 acts as abeamcombiner. The co-aligned images are optionally further reflected andmagnified as desired by first spherical mirror 47-400.

This embodiment also segments the image source 47-030 into a secondforeground image source 47-040 and a second background image source47-080. Second background image source 47-080 is reflected from a secondconventional mirror 47-136 to the second reflective element 47-035.Light from the foreground image source is reflected from the secondreflective element 47-035. Thus, as in other embodiments, secondreflective element 47-035 acts as a beamcombiner. The co-aligned imagesare optionally further reflected and magnified as desired by secondspherical mirror 47-400.

FIG. 49 is a plan view of the multiplayer adapter shown in FIGS. 47 and48. FIG. 49A is a perspective view of the same embodiment. Shown is anadditional optional housing 47-001. Also shown are Light ray 47-106 and47-107. Optional housing 47-001 is provided with an opaque front face47-002.

Light ray 47-106 emits from the first background image source 47-080, isreflected by conventional mirror 47-135 to the reflective element 47-035from which it is reflected to the front of the monitor. Similarly, lightray 47-107 is transmitted by the reflective element and is visible tothe a viewer sitting in front of the monitor. Similar problems occurwith regard to the other player area. The opaque face 47-002 is providedto stop a viewer from having a direct line-of-sight 47-100 with eitherforeground image source.

FIG. 50 is a view of a segmented image source. FIG. 51 is a plan view ofa multiplayer imaging system. FIG. 52 is a perspective view of amultiplayer imaging system.

In FIGS. 50 through 52 there is an image source 50-030. There arereflective elements, which act as beamcombiners. Depicted are a firstreflective element 50-035, a second reflective element 50-036, a thirdreflective element 50-037, and a fourth reflective element 50-038. Imagesource is divided to provide a first foreground image source 50-041, asecond foreground image source 50-042, a third foreground image source50-043, a fourth foreground image source 50-044, as well as a firstbackground image source 50-081, a second background image source 50-082,a third background image source 50-083, and a fourth background imagesource 50-084. Also depicted are a first light ray 50-101, a secondlight ray 50-102, a third light ray 50-103, and a fourth light ray50-104. Also depicted are conventional mirrors used to help co-alignforeground image and background image, namely a first conventionalmirror 50-135, a second conventional mirror 50-136, a third conventionalmirror 50-137, and a fourth conventional mirror 50-138. Depicted are afirst viewer 50-201, a second viewer 50-202, a third viewer 50-203, anda fourth viewer 50-204. Secondary reflective optic 50-401 and 50-402 areoptionally provided.

As seen in FIGS. 51 and 52, light from each foreground section and eachbackground section is co-aligned by the reflective element acting as abeamcombiner and directed to a viewer. Each final scene as seen by aviewer may suffer from a problematic aspect ratio and/or image sizewhich may be corrected through the use of appropriate secondaryreflective and magnifying optics (i.e. an appropriately oriented anddisposed cylindrical Fresnel lens) as taught elsewhere in this document.

First light ray 50-101 is from the co-aligned images from firstforeground image source 50-041 and the first background image source50-081 and is directed to viewer 50-201. Second light ray 50-102 is fromthe co-aligned images from second foreground image source 50-042 and thesecond background image source 50-082 and is directed to viewer 50-202.Third light ray 50-103 is from the co-aligned images from thirdforeground image source 50-043 and the third background image source50-083 and is directed to viewer 50-203. Fourth light ray 50-104 is fromthe co-aligned images from fourth foreground image source 50-044 and thefourth background image source 50-084 and is directed to viewer 50-204.

FIGS. 53 and 54 depict additional light rays 50-105, 50-106, 50-107 and50-108 which represent light which is also combined by the variousreflective elements. For example, viewer 50-204 may see any of theselight rays and therefore may see any of the viewpoints of the otherplayers. It is preferable that a housing having appropriate viewingapertures contain the reflective elements and conventional mirrors. Ahousing with an interior made of dark light absorbing material will helpeliminate ambient light from entering the system, help against internalreflection, and shield the underlying images from undesired output aselsewhere taught in this application.

FIGS. 55 and 56 depict another embodiment of a four-player adapter.There is an image source 55-030. There are reflective elements 55-035,which act as beamcombiners. Image source 55-030 is divided to provideforeground image sources 55-040, as well as background image sources55-080. Also depicted are light rays 55-100. Also depicted areconventional mirrors 55-135 used to help co-align foreground imagesources 55-040 and background image sources 55-080. Viewers 55-200 areshown. Secondary reflective optics 55-400 are provided.

In this embodiment, all of the light rays 55-100 are directed to thefront of the image source 55-030 allowing all viewers 55-200 to sit infront of the television or computer screen.

FIGS. 56A and 56B depict another embodiment of a four-player adapterwherein all images are directed to the front of the image source. Thereis a housing 56-001 and an image source 56-030. There are reflectiveelements 56-035 and 56-036 which act as beamcombiners. Image source56-030 is divided to provide four 3-D views indicated by light rays56-101, 56-102, 56-103, and 56-104. Also depicted are conventionalmirrors 56-135 and 56-135 used to help co-align foreground image andbackground image sets. Fresnel lens 56-300 and secondary reflectiveoptics 56-400 are provided.

Light ray 56-102 and 56-103 are prevented from transmitting throughreflective element 56-035 by housing 56-101. Light ray 56-101 and 56-104are reflected from reflective element 56-036 through Fresnel lens 56-300(which preferably expands and reimages) to the front of the image source56-030. Secondary reflective optics 56-400 (such as a Fresnel mirror,spherical mirror, cylindrical mirror appropriate to restore aspectratio, expand or magnify the image, create a real image, etc. asdescribed in this document) are preferably present.

FIGS. 57 through 59 are plan views of the single image sourcemultiplayer adapter embodiment shown in FIG. 47. Referring now to FIG.57, secondary optic 47-401 has been re-oriented to direct one player'soutput to a position behind the image source.

Referring now to FIG. 58, all secondary optics have been removed. Oneplayer would sits to right of the image source, and the other playersits to the left.

Referring now to FIG. 59, a housing is optionally provided which blockslight from reflective element 47-036 while providing a viewing apertureso that light from reflective element 47-035 may be seen from the frontof image source 47-030.

FIGS. 60 through 62 are plan views of the embodiments shown in FIGS. 57through 59. A Fresnel lens 47-300 has been added to the drawings. It isworth mentioning, that the various adapters as depicted are capable ofutilizing a Fresnel lens (or any other economically and opticallyfeasible lens known to one of ordinary skill in the art) to “float” orcreate real images of any or all image planes involved as taught herein.

The multiplayer adapter desirably provides 3-D real depth in accordancewith the present invention. Alternatively, simplified versions provide2-D images to multiple players, within the scope of the presentinvention.

Single Image Source Non 3-D Multiplayer Adapter

In addition to the various multiplayer 3-D adapter embodiments discussedhereinabove, a multiplayer adapter that uses some of the techniques ofimage redirection described herein.

The same advantages mentioned for 3-D multiplayer adapters—use of aninexpensive image source, excitement of secret perspectives, theglare-free images, etc.—apply as well to the non-3-D multiplayeradapters.

FIG. 63 shows an embodiment of a single image source multiplayeradapter. Depicted are image source 63-030, light ray 63-101, light ray63-102, conventional mirror 63-135, a first viewer 63-201, a secondviewer 63-202, optional secondary reflective optic 63-401 and optionalsecondary reflective optic 63-402.

As pewvioaly taught the image source is divided into multiple portions:a first player portion and a second player portion. Light ray 63-101from a first portion of the screen is reflected from a conventionalmirror 63-135 to a first viewer 63-201 (directly or after interactionwith optional secondary reflective optic 63-401). Light ray 63-102 isdirected to another viewer. The display on image source 63-030 isoptionally compressed 2:1 along one axis to allow an optional secondaryreflective optic to recover the original aspect ratio, albeit at thecost of resolution.

FIG. 64 shows another embodiment of the single-image-source multiplayeradapter of FIG. 63. An additional piece, called a view splitter 63-010,has been attached between each conventional mirror 63-135. Optionalsecondary reflective optic 63-401 has been reversed to redirect lightray 63-101 to a different location. An optional view splitter is used toblock one player from seeing the other player's screen. The angle ofview may be controlled using a view splitter 63-010 or through the useof a Fresnel lens or other means of creating a real image (as taughthereinabove) with a controlled angle of view. Proper placement of aFresnel lens along the path of light ray 63-101 can be used to make surethat a second viewer 63-202 is outside the controlled angle of view.

FIGS. 65 and 66 show an even simpler multiplayer adapter. Depicted arethe image source 65-030, first player portion 65-040, second playerportion 65-042, light ray 65-101, light ray 65-102, optional Fresnellens 65-300, conventional mirror 65-135, a first viewer 65-201, and asecond viewer 65-202. The first viewer 65-201 has a direct line-of-sightto the first player portion 65-040. The output is optionally reimagedand/or enlarged via use of a Fresnel lens 65-300 or other means. Thesecond viewer 65-202 has a reflected view of the second player portion65-042. That portion is also optionally reimaged, magnified ordecompressed using techniques discussed hereinabove. The various partsof the present adapter, unlike many of the embodiments described herein,are not preferably kept in a housing, although some connective means isnecessary to keep the conventional mirror 65-135 properly disposed tothe image source 65-030.

FIGS. 67 through 69 show a non 3-D multiplayer adapter. FIGS. 67 and 68are perspective views, and FIG. 69 is a plan view. The figures showimage source 67-030, first player portion 67-041, second player portion67-042, third player portion 67-043, fourth player portion 67-043, firstlight ray 67-101, second light ray 67-102, third light ray 67-103,fourth light ray 67-104, conventional mirror 67-135, second playerconventional mirror 67-136, third player conventional mirror 67-137,fourth player conventional mirror 67-138, a first viewer 67-201, asecond viewer 67-202, a third viewer 67-203, reference point 67-300, afourth viewer 67-204, and a secondary reflective optic 67-400.

First light ray 67-101 is seen by first viewer 67-201. Second light ray67-102 is reflected from second conventional mirror to second viewer67-202. Third light ray 67-103 is reflected from third conventionalmirror to secondary reflective optic 67-400 to a third viewer 67-204.Fourth light ray 67-104 is reflected from fourth conventional mirror tofourth viewer 67-204.

Additional secondary reflective optics may be used with this embodiment,as with many of the other embodiment discussed in this application.Additionally, a Fresnel lens (or other optic for creating a real image,an enlarged image or an image with a changed aspect ratio) may beincluded at each reference point 67-300 to reimage each player'sperspective, as desired.

FIGS. 70 and 71 show another four-player adapter variant. The figuresshow an image source 70-030, a first player portion 70-041, a secondplayer portion 70-042, a third player portion 70-043, a fourth playerportion 70-044, first light ray 70-101, second light ray 70-102, thirdlight ray 70-103, fourth light ray 70-104, first conventional mirror70-135, second conventional mirror 70-136, third conventional mirror70-137, fourth conventional mirror 70-138, first viewer 70-201, secondviewer 70-202, third viewer 70-203, fourth viewer 70-204, referencepoint 70-300, second reference point 70-301, first secondary reflectiveoptic 70-401, second secondary reflective optic 70-402, third secondaryreflective optic 70-403, fourth secondary reflective optic 70-404.

In this adapter, two of the player portions are directed to the rear,and the other two player portions are directed to the front. Othercombinations of directions are within the variations in design of such amultiplayer adapter or other adapter directing portions of the screen todifferent viewpoints.

The aspect ratio in this embodiment has not been altered. Each playerportion is half as tall and half as wide as the original image source.The appropriate action, if any, to take with additional secondary opticsis uniform magnification. As discussed elsewhere, this may done throughthe us of cylindrical lenses, cylindrical Fresnel lenses, Fresnellenses, spherical mirrors, or any of the cylindrical expansion elementsused in tandem (one to expand the image in the vertical, the other toexpand it in the horizontal). This embodiment illustrates the potentialplacement of spherical mirrors because the spherical mirrors must be agood deal larger than that which they will magnify.

If this embodiment used cylindrical expansion mirrors, then secondaryreflective mirror 70-404 could be placed directly under 70-403 making amore compact system. However, given the size of the spherical mirrorscontemplated in these Figures, the offset is necessary.

FIG. 72 depicts another embodiment of a four-player adapter. Imagesource 72-030, player portion 72-040, conventional mirror 72-135, lightrays 72-100, viewers 72-200, optional reference point 72-300, andoptional secondary reflective optic 72-400 are shown.

As in the other embodiments, light ray 72-100 is reflected to theappropriate viewer 72-200, all of whom sit in front of the image source72-030. Embodiments which direct all output to the front accommodatethemselves well to consumer set-up of their homes: televisions andcomputers are often backed to walls.

Reference point 72-300 shows possible locations for placement of Fresnellenses (or other optical elements for creating a real image with acontrolled angle of view) to provide additional “security” to thoseusing this adapter.

FIGS. 74 through 84 depict a multiplayer adapter. Shown in the figuresare a first view splitter 74-010, a second view splitter 74-011, theimage source 74-030, first player portion 74-041, second player portion74-042, third player portion 74-043, fourth player portion 74-044, lightray 74-101, 74-102, 74-103, 74-104, a conventional mirror 74-135,Fresnel lens 74-300, and secondary reflective optics 74-400.

Referring to FIG. 76, an image source 74-030, such as a televisionmonitor, is placed “face-up.” A view splitter 74-010 is used to createtwo different views, one on each side of the view splitter 74-010. Inthis fashion, one person can see his own portion of the videogame inprivacy, as previously discussed.

A second view splitter 74-011 is preferably slotted or otherwisedetachable from first view splitter 74-010. When the second splitter isin place, this embodiment may be used as a four-player adapter. Eachviewer sits in her own quadrant looking at her respective screen area.

A preferred embodiment of this invention can be seen in FIGS. 79 through81. A conventional mirror 74-135 is angled so as to reflect the firstplayer portion 74-041 to make it easier to view. Viewers may sitcomfortably back from the image source, rather than gazing down on themonitor face itself. This improvement may alternatively be used with thetwo-player version of this embodiment. However, in that instance eitherlarger conventional mirrors are necessary, or it may be necessary to beable to change the orientation thereof to present an integrated image toboth players.

FIGS. 82 and 83 show the addition of Fresnel lens 74-300 (or otherelement that will re-image each light ray into a real image). FIG. 84shows that addition of secondary reflective optics 74-400 can be used toredirect, reimage, and/or magnify the image.

FIG. 84A shows a display system of the present invention. An imagesource 84A-030 is placed “face-up” and its output 84A-101 is directedthrough aperture 84A-001 to secondary reflective optics 84A-401, such asa spherical mirror. Spherical mirrors are relatively cheap to make, andcan be used to uniformly expand images, but must be made larger than theimage that they will expand to reduce spherical aberrations.

FIGS. 85 and 86 show a monitor enlarger of the present invention. Imagesource 85-030, light ray 85-100, first mirror 85-401, and second mirror85-402 are depicted. Referring now to FIG. 85, light ray 85-100 leavesimage source 85-030. Light ray 85-100 is reflected from first mirror85-401 to second mirror 85-402 which expand the image as desired,preferably uniformly. Referring now to FIG. 86, the position of secondmirror 85-402 may be changed to reflect light ray 85-100 to the rear ofthe monitor.

FIGS. 86 and 87 show another embodiment of the monitor enlarger of thepresent invention. Depicted are an image source 87-030, a firstbeamsplitter 87-035, a second beamsplitter 87-036, and a first mirror87-135. Light ray 87-101, 87-102, 87-103, and 87-104, first viewer87-201, second viewer 87-202, third viewer 87-203, fourth viewer 87-204,a beamsplitting mirror 87-401, and a second mirror 87-402, are alsoshown.

Light from the image source 87-030 is reflected from a first mirror87-135. First mirror 87-135 is preferably a cylindrical expansion mirrordesigned to expand the image in one dimension. Light ray 87-101 isreflected from the first mirror 87-135 to the beamsplitting mirror87-401 and further reflected. Preferably, beamsplitting mirror 87-401 isalso a cylindrical expansion mirror disposed to expand the image in itsother dimension. Light ray 87-101 passes to first beamsplitter 87-035,from whence light ray 87-101 continues to a first viewer 87-201, andlight ray 87-102 continues to a second viewer 87-202.

Similarly light ray 87-203 passes through beamsplitting mirror 87-401(and is not imaged in the transmission) until it hits a second mirror87-402. Second mirror 87-402 is also preferably a cylindrical expansionmirror disposed to expand the image in the other direction from firstmirror 87-135. Light ray 103 passes through second beamsplitter 87-036to a third viewer. Light ray 87-104 is a reflected portion of the imagewhich reaches a fourth viewer 87-200.

This adapter allows a single image source to direct output to the fourdirections. While appropriate for some tasks, reading text from theimages could be difficult since each viewpoint sees images which undergoeven and odd numbers of reflections. These problems are fixed using theimage reversal techniques disclosed herein.

In some embodiments employing cylindrical or curved mirrors (orequivalent magnifying optics), the distance of the top and bottom imagesfrom the viewer are different, therefore the magnifications are not thesame. The bottom image often becomes magnified more than the top image,for example. To compensate, the screen is divided so that the one imageis bigger than the other image and the images are the same size afterthey pass through the optical system.

This technology can be used for a movie adapter. The use of a singlecylindrical expansion mirror can help recapture the original dimensionsof a movie and display a full sized image without the black cut-outsfrom letterbox.

An embodiment of the present invention is a “narrow-profile” singleimage source display system. This embodiment uses numerous smallermirrors which decreases the distance the optical elements protrude fromthe image source. These “narrow-profile” embodiments potentially reducesthe apparent distance between the planes, unless some of the methodsdiscussed below are employed to increase the distance between foregroundand background planes. Different embodiments split the screen intogreater or smaller numbers of segments than depicted.

FIGS. 89 to 92 show embodiments of a narrow profile image display systemin which the display is split into numerous foreground and backgroundareas. Each top portion is the foreground portion, and each bottom isthe background portion. Each set of portions is co-aligned as describedhereinabove in the document. The resulting output is striped because nolight passes directly from any background portion. An optionallenticular expansion array is used to expand each image set stripe sogaps or blank stripes are not presented to the user.

Referring in particular to FIG. 89, light 89-101 from each foregroundportion 80-040 passes through a reflective element 89-035, such as abeamcombiner, and then through an optional expansion element 89-400 suchas a lenticular array. Light 89-102 from the background is reflectedfrom a mirror 89-135 (optionally an expanding mirror) and furtherreflected from reflective element 89-035, and then through an optionalexpansion element 89-400.

But for the optional expansion element 89-400, the reflection of light89-102 from the mirror 89-135 would leave dark gaps or stripes. Anoptional expansion element 89-400 is placed to magnify the light imagespassing through it by 2. This doubling eliminates any gaps in the imagecreated by the use of interlaced conventional mirrors.

With a 20″ television set or monitor, a 10-12″ depth between the planesfacilitates the preferred perception of depth. The cylindrical mirrorsare set up so that they create a virtual image 10″ behind a 20″ screen,allowing a very large separation of the planes used for the foregroundand background images.

Referring now to FIG. 90, a curved reflective element 90-035, such as abeamsplitter or partially reflective mirror, is used in front of eachforeground image area 90-040. This displacement has the advantage ofplacing the virtual background image even farther behind the foregroundimage. With a 12″ monitor, for example, each segment would be 0.167″ andthe mirror would therefore have a radius of curvature of 0.25″

FIG. 91, a conventional cylindrical mirror 91-135 is used to reflect thebackground image to a partially reflective cylindrical mirror 91-035which co-aligns the its foreground/background portion set. In thisembodiment, there is even less curvature needed than in FIG. 90, and itis easier to correct for aberrations. Plastic cylinders molded in aframe, then cut and slightly offset could serve as the lens array inthis embodiment. This would be very inexpensive to make, for reasonableimage quality.

In FIG. 92 a second optional expansion element 92-401 (such as a seriesof lenticular lens elements) is used to expand each of the backgroundimage area segments. The expanded image is reflected to the foregroundmirror. Different embodiments split the screen into greater or smallernumbers of segments than depicted.

As with all of the embodiments disclosed in the application, this“narrow profile” 3-D image display system may be used as an image sourcein any of the other image display systems and methods of this invention.As one example, the display output may be reimaged through the use of aproperly placed Fresnel lens (or its reimaging equivalent).

As another example, the display output may be used in combination withother 3-D techniques of this invention in a meta-display system toprovide multiple image planes. Referring now to FIG. 34, the backgroundimage source 34-080 is optionally replaced with a “narrow profile”embodiment as one of many methods to generate multiple image planes.

Time Multiplexing

Time multiplexing has been used to present alternate left- and right-eyestereoscopic views to an observer. With such a system viewers must wearspecial glasses which alternately expose the left and right eyes insynchrony with a display so that each eye sees only the properperspective view. Such a system has all the drawbacks of stereoscopicimaging discussed above, plus it requires twice the normal frame rate toavoid perception of an “alternating eye flicker” which generateseyestrain and headaches in many users.

The invention disclosed herein permits a single image source, such as aTV or computer monitor, to be used to produce foreground and backgroundimages. One way to do this with time multiplexing is by sending theforeground and the background images alternately to the image source.Although it is also preferable here to double the frame rate toeliminate flicker, the standard frame rate is nevertheless lessobjectionable than many other 3-D techniques since both eyes perceiveeach image simultaneously, one behind the other.

The two images can be displayed in their proper locations in space inany of various of ways.

Various means to synchronize the image with a rotating shaft are knownin the art, for example, such means as were used in the CBS tri-colorspinning disk TV system. In some embodiments, the shaft is markedoptically or with an electrical contact so that one rotational positiongenerates a signal to a synchronizing circuit, or the shaft may bedriven by a motor responsive to a synchronizing pulse that is part ofthe decoded TV signal.

When a projector is used to create the image, it may be synchronizedwith the rotating shaft, to provide the nearer and then the fartherimage in alternating succession. These could be successive frames on areel of cinematic film, for example.

When a display is used that provides a successive series of scannedimage frames, such as a TV set or monitor, the system is synchronized toensure that first substantially all the pixels of a particular frame aredisplayed during the time that the screens (or the lens) are positionedto display the near image, and then that the pixels of substantially theentire far image are displayed during the time that the screens (or thelens) are positioned to display the far image.

Where, for example, the rate of scan of a conventional TV picture is 60fields per second, then the shaft is spun at 30 revolutions per second,to provide 30 near images and 30 far images per second. If a systemhaving a different refresh rate is used, the rotational speed issynchronized correspondingly.

Time multiplexing is another way to get “double duty” from an imagesource. Instead of sacrificing resolution (as may be done in some of thesingle-image-source splitting embodiments), full frame foreground andbackground images are displayed on an image source in alternatingsequence.

FIG. 100 shows an image source 100-030, a foreground image projectionscreen 100-040, a background image projection screen 100-080, aprojector 100-300, a lens 100-310, and a rotating member 100-350.

A first image projection screen 100-040 and a second image projectionscreen 100-080 are attached to a rotating member 100-350. Rotatingmember 100-350 is disposed so it alternately presents first projectionscreen 100-040 and second image projection screen 100-080 to projectorlens 310. FIGS. 100A through 100E are elevational views of thisembodiment.

In FIGS. 100A and 100B, the second image projection screen receives asecond image from projector lens 100-310. In FIG. 100C, the first imagescreen 100-040 receives a first image from projector lens 100-310 oncethe rotating member 100-350 has rotated half a turn. The projectionsystem shown in FIGS. 93A through 93C consists of two screens 100-040and 100-080 mounted one hundred eighty degrees apart on a commonrotating member 100-350, each screen at a different distance from theprojector lens 100-310.

As an example, as shown in FIGS. 100B through 100D, a single projector100-300 is used, having a lens 100-310 which has a large enough depth offocus to be in focus on either of the two planes. (Alternatively, twoprojectors could be used, one in focus on each plane.)

In one embodiment, the projection screens 100-040, 100-080 arefront-projection screens, wherein the viewer is located in the vicinityof the projector 300. In that instance, the foreground image appears onthe first screen 100-040, and the background image appears on the secondscreen 100-080. In another embodiment the projection screens 100-040,100-080 are translucent rear-projection screens, wherein the viewer islocated opposite from the projector 300. In that case, the foregroundimage appears on the second screen 100-040 and the background imageappears on the first screen 100-080.

Although the screens 100-040, 100-080 are illustrated diagrammaticallyby rectangles in FIGS. 100B and 100C, they may desirably be shapedotherwise, e.g. in the form of semicircles as shown in FIG. 100D.

Another embodiment, shown in FIG. 100E, uses a pair of completeprojection lenses 100-310, 100-311 in front of the projector on arotating member 100-350, synchronized to the changing position of a pairof projection screens (not shown). Alternatively a projection lens maybe provided that changes focus by the insertion and extraction of a lenselement having a position that is synchronized to the changing positionof a pair of projection screens.

Another time multiplexing embodiment is shown in FIGS. 101A and 101B.Depicted are an image source 101-030, a pair of mirrors 101-040 and101-041, light rays 101-101 and 101-102, a viewer 101-200, and arotating shaft 101-350. The image source 101-030 is preferably a singleTV monitor. The images are viewed in a spinning mirror arrangement. Thisembodiment comprises a pair of mirrors 101-040 and 101-041, mounted onehundred eighty degrees apart, on a single rotating shaft 101-350. As themirrors 101-040 and 101-041 alternately rotate into position to presentto the viewer 101-200 a virtual image of the monitor 101-030, the viewer101-200 sees with both eyes, alternatingly a more distant image (whenthe system is in the position shown in FIG. 101A) and then a closerimage (see FIG. 101B) followed by the next version of the more distantimage (see again FIG. 101A). The two alternating light paths from themonitor to the viewer are shown by dashed lines 101-101 and 101-102.

FIGS. 102A and 102B show a perspective view of another embodiment. InFIGS. 102A and 102B, depicted are a large lens 102-300, stationaryprojection screen 102-030, a projector 102-031, real image 102-050, anda viewer 102-200.

Alternately, as shown in FIGS. 102A and 102B, a large lens 102-300, suchas a Fresnel lens, cut to form a semi-circle, is made to rotate in frontof a stationary projection screen 102-030. The viewer 102-200 sees theprojection screen successively through the lens (as shown in FIG. 102B)and then directly (as in FIG. 102A). When the lens 102-300 is in frontof the screen 102-030, the screen 102-030 is made to appear closer tothe viewer (and larger), in the form of a real image 102-050. This is aforeground image. When the lens is rotated away from this position, thescreen 102-030 appears at its actual distance (and smaller), see FIG.102A, as the background image. The lens 102-300 position is synchronizedto the images that are projected onto the screen by projector 102-031.The screen may be a front-projection screen positioned so that theprojector beam does not go through the lens. However it is preferably arear-projection screen, as shown.

Neither “letterbox” nor “portrait” is the shape of a traditional TVmonitor. It would be more difficult to re-map a traditional TV image toan overly wide or tall screen. Or, if the re-mapping were done topreserve proportion and faithful reproduction, a much smaller area ofthe screen would be used, as superfluous height or width would betrimmed.

The “proportioned” orientation requires placing the TV monitor on itsside. Proportion is preserved, but the user is required to turn the TVset on its side. That may be inconvenient in some instances, forexample, where the TV is used for both game playing and traditional TVviewing.

The major advantage of the “proportioned” orientation is that theforeground and background sections have proportions that more closelyapproximate that of a full screen. Thus it is unnecessary to design forthe screen shape generated by the adapter; instead, the video signal canbe produced generically and viewed by some viewers using customary 2-Dtelevision screens and by others using apparatus of the presentinvention, with minimal information regarding depth being required toget full 3-D effect from the adapter, as previously discussed.

Of course, all problems with aspect ratio caused by the splitting of thescreen can be cured through the use of elements that expand an imagealong a desired line.

In addition, in some of the embodiments foreground image and backgroundimage are created to be of different sizes.

Real Image Monitor

Embodiments of the present invention preferably provide 3-D real depthin accordance with the present invention. Alternatively, a simplifiedversion provides a real image of an image source within the scope of thepresent invention. One embodiment of the present invention that formsreal images uses a Fresnel lens (or other means of generating a realimage as known in the art and/or discussed herein) and a mirror in ahousing. The housing has holes or apertures: a rear aperture that sitsmore or less flush with the image source (for example, the face of aCRT) and a second aperture through which the real image is viewed.

The image is reflected from the mirror (which is angled appropriately,desirably at a 45-degree angle) and through the Fresnel lens, whichfocuses the light into a real image. This real image appears to float inspace.

Like other indirect viewing systems, an advantage of the presentinvention is that the user is further from the computer monitor and itsassociated hazards. In addition, the indirect viewing system of thepresent invention has certain advantages over other prior art viewingsystems in that a angle of view is controllable and there is a greatreduction in glare. Both features would be useful, for example, in anoffice setting or at an automated teller machine, where privacy isimportant and where glare is potentially distracting.

Recording

According to the present invention a number of techniques may beemployed in imaging processing methods for processing source imagescomprising live or pre-recorded images to be displayed using the displaytechniques of the present invention. These techniques and methods varyin accordance with whether the source image is a live image or is analready recorded and stored image to be displayed according to thedisplay methods of the present invention.

The image processing methods of the present invention process a sourceimage to view using the display techniques of the present invention.These display techniques utilize at least two separate images, usuallyincluding a foreground image and a background image, separatelydisplayed on at least two separate optically aligned planes or volumes.The source image is either a live scene characterized by a continuousthree-dimensional space defined between a forwardmost foreground objectand a rearmost background object or a pre recorded two-dimensional imagedisplayable on a single plane and containing the same human visual depthperception cues contained within a photograph.

Each source image is divided into at least two image signals. Theseseparate image signals produce separate images on different portions ofa single image display device which are then optically combined to forma composite image scene or other display, or are used to synchronouslygenerate a plurality of images each on a separate display device whichare then optically combined to form the composite image scene or otherdisplay.

There are several image capture techniques which may be employed inaccordance with the present invention to capture live images. Accordingto a first image capture technique useful for capturing images to bedisplayed using the present invention, a first camera is directed at oneor more foreground objects in a scene to be captured. The function ofthe first camera is to capture the foreground of the scene. A secondcamera is positioned behind or above the foreground subject matter andis also directed at the scene to be captured. The function of the secondcamera is to capture the background of the scene.

Numerous configurations for the relative positioning of the two camerasmay be employed. For example, both cameras can be located in the sameplane, one being vertically positioned at chest height and the secondbeing vertically positioned about ten feet or so higher than the firstcamera and aimed downward. Due to the position and lens characteristicsof the second (higher) camera, foreground objects would be outside ofits field of view. The first and second cameras would be equipped withdifferent focal length lenses, the focal length of the lens on the firstcamera being selected to focus on objects in the foreground and the lensfor the second camera being selected to focus on objects in thebackground of the scene. The depth of field of the first camera may beselected to focus on a range of objects in a Z depth corresponding tothe depth of foreground composition and the depth of field of the secondcamera may be selected to focus on a range of objects in a Z depthcorresponding to the depth of background composition. Other numbers ofcameras may be employed.

According to the present invention, techniques are presented to minimizeor eliminate the background information from the foreground image.Several techniques are available to accomplish this task. In theembodiment where the first camera is focussed on the foreground subjectmatter and the second camera is focussed on the background subjectmatter, one of several known focus detection algorithms may be employedto eliminate the out-of-focus subject matter from each image. As anexample, known focus detection systems utilize spatial frequencydetection, contrast level detection, or Modulation Transfer Function(MTF) threshold detection.

This technique is also useful for processing prerecorded images in, forexample, two-dimensional movie subject matter. A focus threshold isselected and everything greater than the focus threshold is consideredto belong in the foreground image and everything less than the focusthreshold is considered to be in the background image.

Another multicamera technique which is contemplated for use inprocessing images for display according to the present invention is toemploy two or three cameras horizontally displaced from one another,e.g., one to capture the scene from the left, one to capture the scenefrom the center, and one to capture the scene from the right. Thedifferent angles of view allow a composite full view of all backgroundobjects behind the one or more foreground objects in the image.

Yet another multicamera technique comprises two horizontally-displacedcameras arranged in parallel fields of view at the same Z location. Thetwo images generated by the two cameras are compared and matchingobjects from each image can be recognized using known computer matchingtechniques. Matching objects are recognized and the distance from theimage of each object to the edges of the frame in each of the two imagesare calculated to determine depth. At infinity, all objects overlap, butas objects get closer to the cameras, the corresponding images becomeseparated by greater distances.

Those of ordinary skill in the art will recognize that variations ofthis technique are possible. In one variation, the cameras are aimed ata common point such as the center of the furthest background object. Allobjects at that point will be aligned and closer objects will becomeseparated. This technique also works when the cameras are verticallydisplaced. Vertical camera displacement may be advantageous when dealingwith scenes which are horizontally cluttered.

Computer processing of the image signals may then be performed toselectively eliminate background objects or areas using techniques suchas have been employed in colorization of motion pictures (in which thecomputer tracks a selected object or area from frame to frame) to createthe foreground image frame. Where real-time processing is not an issue,foreground objects can alternately be selected by hand. The sametechniques can be used to produce a background image devoid offoreground objects.

A single-camera technique for identifying foreground and backgroundobjects according to the present invention employs two lenses which arefocused on the same scene through a single aperture by way of abeamsplitter One lens is focused on the foreground and the other isfocused on the background and each lens focuses an image on its ownimage detector. By using known techniques which discard out-of-focuscomponents, foreground and background objects can be identified andeliminated from each of the foreground and background images asrequired. Known fill techniques may be used to reconstruct backgroundareas occluded by foreground objects.

In situations requiring real-time processing, the computer may selectforeground objects on the fly. One technique for facilitating thisseparation is to employ a camera whose sole purpose is to captureforeground objects. This camera is set for a narrow depth of field, andstandard techniques may be employed to select in-focus objects from thescene foreground. Another technique which may be usefully employed toselect foreground images “on-the fly” is to analyze the spatialfrequency of the various portions of the image. Spatial frequency willbe highest for in-focus objects. A spatial frequency threshold isselected and groups of pixels having a spatial frequency above thresholdare determined to belong to foreground objects.

Another technique which can be employed to discriminate betweenforeground and background objects is contrast detection. Highestcontrast areas are generally found in foreground objects. Techniquessuch as MTF filtering look for the highest difference between dark andlight areas of an image.

Because objects in the foreground of an image generally move morequickly than objects in the background, frame-to-frame motion detectioncould also be employed to discriminate between foreground objects andbackground objects. Another useful technique which may be employed todistinguish between foreground and background objects is colorsaturation which decreases as objects recede into the background. Otheruseful techniques include brightness detection, based on the assumptionthat closer objects are usually brighter. Optical subtraction may beemployed with these techniques to eliminate portions of the image thatare the same in successive frames, resulting in an image of foregroundobjects.

Those of ordinary skill in the art will appreciate that combinations ofthe above techniques may be employed. The limitation of any singletechnique or combination of techniques is most critical when processinglive images, due to the processing bandwidth limitation of theprocessing hardware. This limitation is not a consideration whenprocessing already recorded two-dimensional images.

In some image compositions, there are instances when background objectsare blocked by foreground objects at all camera angles. In suchsituations, commonly known computer graphics replication techniques mayemployed to fill in dead spots in background areas caused by obscuringforeground objects. One such technique is particularly useful when amoving foreground object is blocking a background area. Different areasof the background will be blocked in successive frames of the image. Bystoring the successive frames, the blocked background areas may bereconstructed by using selected background data from different framesusing known techniques.

In addition, ranging techniques may be employed during capture of liveimages. For example, a coherent or incoherent projected grid may besuperimposed on the scene in a way in which it will not show up in therecording of the image. Examples of such grid projection techniquesinclude infrared or ultraviolet projection and scanning or strobing at afrequency or speed that will not be recorded with the image. A detectormay be gated to the grid flash (with the camera gated oppositely to theflash). The grid may be detected and its focus analyzed. Thresholdconditions may be used to determine if an object is in the foreground.If the imaged grid pattern is scanned in synchronization with a scenescanning camera, the Z coordinate can be approximated for each elementin the scene and can be stored with the pixel to use to separateforeground and background. This technique may be performed on a percamera basis where multiple cameras are employed.

When the grid is projected onto an object, the size of each grid lineand grid square is proportional to the projected distance from thesource to the object. In addition, when the grid is projected onto athree dimensional surface of an object, the grid lines each becomedistorted as a function of the Z position of each point on the threedimensional surface. The computer can employ known techniques to analyzea two dimensional scan of the projected grid lines to determine the Zcoordinate of each point on the surface.

Another scanning technique applicable to the present invention is toscan the scene with a laser beam and detect the reflection from objectsin the scene. The reflected spot size is proportional to the distancetraveled by the reflected beam due to the limited depth of focus of thelens.

Another laser technique employs a scanned laser beam that is pulsed forshort periods of time. The laser is configured to have a coherencelength within which all foreground objects reside. When the beam isreflected from an object in the scene, the reflected beam is receivedand recombined with a reference beam from the same laser, and aninterference pattern will develop only for objects which reside withinthe coherence length. A detector is used to detect the presence of theinterference pattern. This technique identifies objects in theforeground. If the camera used is scanning the scene in synchronizationwith the laser beam, each pixel in the scene can be identified as comingfrom a foreground object or a background object by storing an additionalbit with the pixel. Known object-detection techniques, such as analyzingpixels to find boundaries (large changes) which define the edges of anobject, can be utilized to store Z-coordinate information for entireobjects rather than for each individual pixel, reducing the amount ofZ-coordinate data that must be stored or transmitted for each frame.

The grid generation and laser scanning techniques disclosed herein maybe augmented by employing two or more spaced apart grid generators orscanning laser beams to avoid the problem of foreground objects blockingthe grid or laser beam from reaching objects or areas.

Software and Hardware Image Solutions

As will be appreciated by those of ordinary skill in the art, methodsare provided for preparing source images to be displayed according tothe present invention. Software may be used to process source images togenerate displayed images according to the present invention. There areseveral steps performed by software according to the present inventionto process source images into displayed images according to the presentinvention. The manner in which any single step of the methods performedby software herein is performed may be any known manner to perform suchstep.

According to a method of the preset invention, source images are dividedinto at least two images, at least one foreground image and at least onebackground image. Techniques for dividing source images are known andhave been mentioned herein. When both foreground and background imagesare displayed on the same display device, the computer or other devicewriting to the display device must be configured to write the foregroundimage to a first designated area of the display device and to write thebackground image to a second designated area of the display device. Forexample, if a raster-scanned CRT display is employed, the foregroundimage may be written to the top half of the CRT and the background imagemay be written to the bottom half of the CRT by supplying the pixel datafor the foreground image during the first half of each display frame andsupplying the pixel data for the background image during the second halfof each display frame. Implementation of such a display scheme istrivial for CRT and other display devices, involving only providing thecorrect data at the correct time.

If the plurality of divided images are formed on a single displaydevice, such as a CRT display, it may be desirable to employ opticalexpansion during viewing of at least one of the images to recreate theaspect ratio of the original image. In the event that optical expansiontechniques are employed, it is advantageous to display the imagecompressed in the direction which is to be expanded, e.g., vertically.Such compression according to the present invention allows opticalexpansion without resulting in a stretched image in that direction.Image compression techniques are well known in the art and have beenembodied in software.

In this regard, resolution enhancement steps may be performed on imagedata if the image is to be optically expanded to restore aspect ratio.Numerous known pixel and line interpolating methods may be employed forthis purpose.

According to one method of the present invention, perspective of a scenemay be exaggerated to make the scene appear more three dimensional.Objects in the background image of the scene may be shrunk relative toforeground objects according to the present invention to exaggeratedepth perception. Background image objects may be easily shrunk withoutloss of resolution according to known methods, which may also includethe step of expanding foreground objects, shrinking background objectsor performing both steps. Exaggerated reduction and elongation of partsof foreground images will make them appear to fill the space between theforeground and background planes.

Because the image display techniques of the present invention utilize atleast two overlapping images, it is advantageous to control thebrightness of the background and foreground images in order to preventbackground images from “bleeding through” images of foreground objects.Brightness control techniques are employed in accordance with thepresent invention to prevent background images from bleeding through tothe foreground. One method according to the present invention is togenerate a shadow of a foreground object at a location in the backgroundimage corresponding to the location of the object in the foregroundimage. This method lowers the light level at that point in thebackground image to minimize background image bleed through. The shadowis preferably somewhat larger (e.g., about twice the size in eachdirection) than the foreground object, and is preferably tapered, i.e.,made darkest in its enter and lighter towards its edges to preventunnaturally abrupt brightness transitions in the background image. Inthis manner, parallax artifacts between the foreground and backgroundimages are minimized. Alternatively, the brightness of the entirebackground image may be reduced, and/or the brightness of the foregroundimage increased for the same end.

Another brightness control technique which may be employed according tothe present invention to prevent background image bleed through is colorbalancing. Since darker colored foreground objects are more susceptibleto bleed through from brighter background objects, color brightnesscomparisons may be made between corresponding regions of the foregroundand background images, and hues of foreground objects can be brightenedas necessary and background colors can be darkened as needed. It is alsocontemplated to increase the brightness values of selected foregroundobject pixels according to this method. Use of either or both techniquesresults in an increased difference between the brightness of foregroundand background objects to reduce or eliminate background bleed-through.

The display technology of the present invention as disclosed hereinincludes the use of light valves disposed in a conjugate plane of theforeground image located in the background image path to blockbackground light which would otherwise bleed through foreground objects.According to this aspect of the invention, a light valve device, such asa binary LCD array permits selective transmission or blocking of regionsof the background image by producing silhouettes of foreground objectsto block background light from passing through to the viewer with noparallax error. According to one method of the present invention, shadowimages of foreground objects are generated on the light valve elementsto create the shadow image of foreground objects. This method accordingto the present invention uses known techniques to create a black pixelon the light valve plane wherever there is a non-zero (or otherthreshold) pixel value of the foreground image.

The perception that a displayed object is undergoing Z-axis motion,i.e., receding into the background or proceeding into the foreground,may be enhanced according to the present invention by plane-switchingtechniques. Such techniques include the steps of gradually decreasingthe size of the object as it recedes in the Z direction and, at aselected time, moving the image of the object from the foreground imageto the background image. Likewise, objects in the background image whichare moving in the Z direction towards the viewer may be graduallyincreased in size and at a selected point are transferred from thebackground image to the foreground image. This effect may be implementedon a frame by frame basis using known image processing techniques.

According to another aspect of the present invention, the foreground andbackground images are temporally synchronized. This method may beimplemented using known techniques and is especially useful where twoindependent image sources, such as CRT displays or projectors, areemployed.

According to certain embodiments of the display techniques of thepresent invention, one or more images are reversed as a consequence ofhaving been reflected from an odd number of mirrors. When preparingimages for display on such display embodiments of the present invention,this image reversal may be corrected by generating a reversed image sothat subsequent reversal of that image by reflection from an odd numberof mirrors will result in an unreversed image. Known techniques, such asCRT scanning from right to left, or display pipelining lines of pixeldata from right to left, may be employed for this purpose.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects as illustrative and notrestrictive. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope. Theinventor intends that all patentable subject matter disclosed hereineventually be the subject of patent claims, regardless of whetherpresented upon the initial filing of the application represented by thisdocument or in a subsequent filing.

1. An image display system comprising: a composite image source, a firstportion of the composite image source depicting foreground imageelements, and a second portion of the composite image source depictingbackground image information; a beam combiner; and abackground-image-occluding element; wherein said first portion of saidcomposite image source, said second portion of said composite imagesource, and said beam combiner are so disposed as to present to a viewersaid foreground image elements from said one of said composite imageportions at a shorter distance from the viewer than said backgroundimage information presented to the viewer from said other of the saidcomposite image portions, and wherein said background-image-occludingelement is located at a distance from the viewer that is opticallyequivalent to the distance between the viewer and said foreground imageelements.
 2. The image display system of claim 1 wherein saidbackground-image-occluding element is a light valve such as an LCD. 3.An image display system comprising: at least two image sources, a firstimage source depicting foreground image elements, and a second imagesource depicting background image information; a beam combiner; and abackground-image-occluding element; wherein said first image source,said second image source, and said beam combiner are so disposed as topresent to a viewer said foreground image elements from said one of saidimage sources at a shorter distance from the viewer than said backgroundimage information presented to the viewer from the other of the saidimage sources, and wherein said background-image-occluding element islocated at a distance from the viewer that is optically equivalent tothe distance between the viewer and said foreground image elements. 4.The image display system of claim 3 wherein saidbackground-image-occluding element is a light valve such as an LCD.